r 


REESE  LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 

Jl&<2/*&w 

Accession  No.  /  ^/  /  9    .    Class  No. 


a^oB^v^^ 

5m 


I 


. 


' 


HINTS 


—  ON- 


AMALGAMATION 


AND    THE 


GENERAL  CARE  OF  GOLD  MILLS 


BY 


W.  J.  ADAMS,  A.  M.,  E.  M. 

»  i 

Graduate  of  the  School  of  Mines  of  Columbia  University, 
New  York. 


A  REFERENCE  BOOK  OF  ACTUAL   GOLD-MILL  PRACTICE, 
DETERMINED  BY  AN  EXPERIENCE  OF  TWENTY  YEARS 
WRITTEN  IN  LANGUAGE  THAT  CAN  BE 
UNDERSTOOD  BY  ALL. 


ILLUSTRATED. 


CHICAGO: 
MODERN  MACHINERY  PUBLISHING  COMPANY. 


Entered  According  to  Act  of  Congress  in  the  Year  1898, 

BY  W.  J.  ADAMS. 
In  the  Office  of  the  Librarian  of  Congress  at  Washington,  D.  0. 

19//9 


TABLE  OF  CONTENTS. 


Page. 

Introduction 7 

Chapter  1 — General  Process 11 

Arrangement  of  Mortars 17 

"   Plates 21 

"              "    Concentrators    ....  30 
"            for  Canvas  Plant      ....  34 

"         2 — Care  of  Quicksilver v  *.  \ 35 

Amalgamation 43 

"         3— Cleaning-up 60 

4— Retorting  and  Melting 73 

"         5 — Concentration 85 

6— Sampling 98 

7-  Conclusion  108 


UNI".  Y 


INTRODUCTION. 

Gold  has  been  known  from  the  earliest  ages,  from  its 
occurrence  in  a  metallic  state  in  sedimentary  deposits 
as  well  as  in  veins.  On  account  of  its  great  specific 
gravity,  it  can  be  collected  from  placers  and  river  beds, 
by  separation  with  water  alone,  and  in  veins  after  the 
matrix  is  crushed,  a  great  amount  is  saved  by  the  same 
simple  method.  When  only  rich  deposits  were  exploited, 
anybody  could  manage  as  it  apparently  required  only 
labor  and  opportunity,  while  as  long  as  money  was 
made,  the  losses  that  occurred  did  not  trouble  the  own- 
ers. From  this  very  simplicity  of  working,  the  major- 
ity of  owners  and  investors  imagined  that  no  special 
training  was  requisite  to  insure  success,  but  that  any 
trustworthy  man,  skilled  in  mercantile  pursuits,  was 
the  proper  person  for  the  place  of  general  manager. 
To-day  the  same  opinion  is  held  by  very  many,  in  spite 
of  the  warnings  from  hosts  of  disastrous  failures.  One 
cause  for  this  belief  has  been  the  lack  of  literature  for 
this  special  branch  of  metallurgy;  in  fact,  very  near 
1890,  there  was  practically  no  works  written  at  all 
which  spoke  of  gold  except  as  a  subsidiary  product 
of  the  metallurgy  of  other  metals.  Volumes,  both  prac- 
tical and  scientific,  have  been  published  which  deal  with 
the  special  branches  of  the  metallurgy  of  lead,  copper, 

7 


8  HINTS  ON  AMALGAMATION. 

and  silver,  but  the  metallurgy  of  gold  seemed  so  simple, 
it  only  required  an  occasional  article  in  a  paper  or 
magazine. 

In  spite  of  this  dearth  of  written  knowledge,  practical 
men  in  all  parts  of  the  world  were  rapidly  improving 
the  methods  of  treatment,  both  mechanically  and  with 
the  aid  of  chemistry,  in  their  several  localities;  but, 
through  lack  of  exchange  of  thought,  each  section  had 
a  different  process,  on  which  faith  was  pinned  to  the 
exclusion  of  all  other  processes. 

As  the  rich  deposits  gave  out,  attention  was  turned 
to  those  of  lower  grade,  which  are  now  found  to  be  very 
profitable  with  improved  machinery  and  increased 
knowledge,  but,  even  to-day,  we  are  in  the  infancy  of 
this  science.  The  treatises  on  gold,  now  before  the 
public,  can  still  be  counted  on  the  fingers  of  one  hand, 
and  are  either  devoted  to  the  scientific  discussions  of 
processes  now  in  vogue,  the  history  past  and  present 
of  gold  milling,  or  the  mechanics  pure  and  simple  of  the 
various  machinery  used.  They  are  all  good  for  the  edu- 
cation of  the  world,  but  are  lacking  in  definite  direc- 
tions of  the  best  way  to  employ  the  methods  they 
describe,  and  are  generally  understood  by  those  only 
who  have  enjoyed  a  previous  technical  education.  This 
absence  of  intelligent  application  of  these  known  prin- 
ciples in  the  great  majority  of  the  mills  in  this  State 
(the  home  of  gold  milling),  has  been  a  constant  source 
of  wonder  to  me,  and  yet  I  have  a  fellow  feeling  from 


"    HINTS  ON  AMALGAMATION.  9 

my  first  experiences  in  gold-mill  practice.  Graduating 
from  a  celebrated  school  of  mining  engineering,  I 
thought  myself  eminently  fit  to  at  once  assume  the 
absolute  management  of  the  biggest  mining  concern  on 
earth,  but,  thanks  to  the  kind  influence  of  an  elder 
brother,  already  well  known  in  the  mining  world,  1 
was  started  at  the  bottom  of  the  ladder  in  a  gold  mill, 
to  begin  my  real  education.  I  very  soon  found  that 
there  was  no  bigger  tenderfoot  in  California,  as  my 
technical  education  had  only  taught  the  chemistry  and 
scientific  mechanics  in  general,  with  no  practical  rules 
of  how  to  apply  this  knowledge.  These  practical  rules 
have  been  learned  through  bitter  experience,  extending 
through  many  years,  and  to  try  and  help  others  who  are 
just  beginning,  I  have  set  down  in  the  following  pages 
the  results  of  the  observations  I  have  made,  all  of  which  ' 
have  been  practically  demonstrated  as  correct  by  appli- 
cation on  several  very  difficult  ores,  with  marked  suc- 
cess in  every  case.  It  has  been  a  work  of  pleasure  to 
contribute  this  mite  of  knowledge,  and  if  I  am  instru- 
mental in  increasing  the  production  of  only  one  gold 
mill,  I  will  feel  amply  repaid  for  my  labor. 

I  ask  the  indulgence  of  the  reader,  to  overlook  the 
absence  of  rounded  sentences  and  polished  language, 
and  take  the  will  for  the  deed.  I  have  done  the  best 
I  am  able,  and  can  only  leave  the  verdict  to  the  public. 

W.  J.  ADAMS,  E.  M. 

San  Francisco. 


CHAPTER  I. 
GENERAL  PROCESS. 

It  is  not  the  purpose,  in  this  book,  to  enter  into  any 
detailed  description  of  "gold  milling,"  as  the  ground  has 
already  been  amply  covered  by  E.  B.  Preston,  in  his  re- 
port on  "Gold  Milling,"  published  by  the  "State  Min- 
eralogist," of  California. 

Some  other  points  also  may  seem  too  well  known  and 
appreciated  to  be  mentioned,  but  these  require  con- 
stant repetition,  and  even  then  very  little  practical  ap- 
plication seems  to  be  made  by  the  average  millman. 
Q[n  order  clearly  to  understand  the  entire  method,  we 
must  start  with  the  ore  as  it  comes  from  the  mine.  This 
ore  must  first  be  carefully  examined,  as  its  character 
and  structure  as  well  as  its  value,  determine  the  most 
advantageous  method  to  pursue.  First,  the  ore  may  be 
hard  and  tough,  requiring  force  to  disintegrate  it,  though 
entirely  free-milling;  second,  the  ore  may  be  soft,  giving 
a  great  deal  of  slimes;  third,  the  ore  may  be  a  mixture 
of  the  above  two  divisions. 

First:  Here,  the  ere  is  first  dumped  over  a  grizzly, 
with  the  bars  set  1%  inch  apart,  the  coarse  lumps  going 
through  a  rock-breaker  of  some  form,  to  mix  with  the 
fines  in  the  ore  bin.  From  this  bin  it  must  be  carried 
to  stamps,  preferably  of  heavy  weight,  notwithstanding 
all  assertions  to  the  contrary  by  patentees  and  makers 
of  other  pulverizing  devices  which  are  "just  as  good  as 
stamps." 

Second:  When  the  ore  is  soft,  it  also  requires  to  be 
passed  through  a  breaker,  to  enable  the  particles  to  be 

11 


12  HINTS  ON  AMALGAMATION. 

of  uniform  size;  but  here,  very  frequently  any  kind  of 
stamp,  and  always  those  of  heavy  weight,  will  slush 
through  the  bed  of  pulp,  wearing  out  iron  uselessly,  and 
increase  the  proportion  of  slimes,  always  to  be  avoided 
as  much  as  possible.  Here  we  find  a  great  advantage  in 
the  different  types  of  the  Chilian  mill,  such  as  the  Hunt- 
ington  and  Bryan,  from  both  of  which  the  pulp  escapes 
as  soon  as  it  is  reduced  to  the  requisite  size,  as  de- 
termined by  the  screen,  and  with  the  minimum-  of  slimes 
to  hinder  future  operations. 

Third:  In  an  ore  containing  both  soft,  clayey  or  talcose 
material,  and  hard  bunches  of  quartz,  stamps  are  gener- 
ally the  best,  as  the  grit  of  the  hard  quartz  prevents 
pounding  of  iron  on  iron,  and  causes  sufficient  splash  to 
keep  the  screens  from  choking,  while  all  operations  can 
be  kept  under  close  observation,  which  cannot  be  done 
with  any  pan  or  roller  mill— one  of  the  greatest  objec- 
tions to  the  general  use  of  these  mills.  In  some  few 
cases,  however,  where  the  output  from  the  mine  is  suffi- 
ciently large  to  wrarrant  the  outlay  of  capital,  it  will  be 
found  of  great  benefit  to  separate  the  ore  partially  and 
automatically  into  two  classes.  Dumping  the  ore  over 
a  long  grizzly,  the  soft  and  fine  will  go  into  one  bin, 
while  the  coarse,  after  being  put  through  the  breaker, 
falls  into  a  second  bin.  That  from  the  first  bin  is  fed  to 
one  or  more  roller-pan  miJn,  while  the  hard  broken 
quartz  goes  to  the  stamp  mill,  very  largely  increasing 
in  this  way  the  output  through  the  two  methods  com- 
bined. 

The  pulverized  ore,  technically  known  as  "battery 
pulp,"  is  now  carried  by  water  down  silver-plated  copper 
plates,  by  which  means  as  much  of  the  gold  as  possible 
is  abstracted,  varying  very  considerably  under  different 
millmen's  methods;  a  low  percentage  saved,  being  ex- 


HINTS  ON  AMALGAMATION.  la 

cused  by  such  terms  as  "floured  gold,"  that  floats  in 
water,  rusty  gold,  "plumbago  in  the  ore,"  or  a  similar 
state  of  affairs. 

However,  there  is  generally  sufficient  gold  left  in  this 
pulp,  which  could  never  be  saved  with  quicksilver,  to 
require  further  treatment,  while  the  value  is  too  low  to 
treat  all  the  pulp  en  masse.  This  gold  is  either,  me- 
chanically or  chemically,  locked  up  with  other  metal- 
liferous substances,  generally  sulphides  or  minerals  of  a 
higher  specific  gravity  than  the  accompanying  gangue. 

This  specific  gravity  is  the  keystone  to  all  the  con- 
centrating devices,  and  the  special  method  required  is  de- 
termined by  only  two  facts,  the  value  of  the  concentrates 
when  pure,  and  the  percentage  of  them  carried  by  the 
ore.  Should  these  concentrates  be  of  low  value  and  mod" 
erately  coarse,  a  simple  bumping  table,  like  the  Gilpin 
County  bumping  table,  or  its  improvement,  the  Wilfley, 
could  be  used,  as  they  require  little  care,  are  reasonable 
in  price,  and  save  concentrates  free  from  foreign  mat- 
ter, while  the  final  tailings,  though  still  carrying  a  large 
percentage  of  mineral,  will  be  economically  valueless 
owing  to  the  intrinsically  low  value  of  the  sulphurets. 
When,  however,  the  concentrates  are  of  value,  for  in- 
stance above  $50  per  ton,  a  mechanism  of  much  greater 
delicacy  must  be  employed,  and  of  all  the  devices,  none 
has  proved  so  satisfactory  as  an  endless  moving  belt, 
shaking  without  a  jar.  As  a  rule,  the  higher  the  grade 
of  sulphurets  the  more  friable  they  are,  and  the  finest 
slimes,  most  easily  affected  by  agitation,  carry  the  rich- 
est particles,  reaching  a  culmination  in  the  tellurides. 
Should  the  "battery  pulp"  carry  a  high  percentage  of 
sulphurets,  that  is,  above  12  per  cent.,  it  very  often  be- 
comes necessary  to  use  a  double  concentration,  and  in 
this  case  two  machines  of  the  same  type  are  used,  the 


14  HINTS  ON  AMALGAMATION. 

tailings  from  the  first  passing  directly  to  the  second, 
after  removing  the  surplus  water  if  there  is  too  much 
added  on  the  first  machine. 

In  spite  of  all  these  precautions,  it  is  very  frequently 
found  that  the  concentrator  tailings  still  carry  an  ap- 
preciable value,  and  most  thorough  tests  must  be  made 
to  determine  whether  or  not  this  can  be  economically 
saved.  The  first  and  commonest  method  is  to  allow  the 
tailings  to  run  over  a  large  surface,  covered  with  canvas, 
which  is  cleaned  and  swept  several  times  a  day,  but, 
generally,  this  only  saves  a  small  percentage  of  the  loss, 
and  its  only  advantage  is  its  cheapness.  With  proper 
care  and  experience  the  concentrators  should  save  all 
that  the  canvas  plant  could  do,  and  any  further  reduc- 
tion must  treat  economically  with  the  entire  mass. 

So  far  the  only  way  to  do  this  is  by  employing  some 
of  the  modifications  of  the  "cyanide  process,"  and  this 
requires  a  large  tank  capacity,  so  that  the  tailings  can 
flow  directly  to  the  filtering  tanks.J 

This  is  concisely  the  method  of  gold  milling,  but  there 
are  several  points  to  observe,  to  insure  complete  success 
on  the  majority  of  ores. 

First,  foremost  and  at  all  times  is  the  question  of 
grease.  Guard  against  its  excessive  use  day  and  night, 
month  and  year.  Keep  all  the  bearings  and  machinery 
where  it  is  used  as  scrupulously  clean  as  a  New  En- 
gland housewife  does  her  home;  do  not  grudge  the  use 
of  clean  waste,  but  see  that  the  employees  observe  the 
maximum  of  cleanliness.  Bits  of  candles  do  no  harm, 
or  very  little,  if  made  of  stearic  acid,  but  beware  of 
tallow  dips.  Start  in  with  the  rock  breaker,  and  place 
dripping  pans  underneath  the  journals,  making  frequent 
examinations  to  see  that  all  the  drops  are  caught.  See 
that  none  of  the  oil  used  on  the  running  gear  of  the 


HINTS  ON  AMALGAMATION.  15 

self -feeders  drops  on  the  feeder  floor,  being  very  careful 
about  working  the  leakage  of  ore  always  found  under- 
neath the  feeders,  if  there  is  the  slightest  possibility 
of  its  being  fouled.  Clean  the  stems  of  the  stamps,  the 
cams  and  tappets  very  frequently,  and  do  not  use  liquid 
oil  on  them,  but  make  a  swab  of  blanket  and  apply  a 
minimum  of  axle  grease,  to  the  cams  several  times  a 
day,  to  the  stems  only  as  needed.  When  applied  to  the 
stems,  only  touch  them  above  the  guides.  It  is  gen- 
erally better  to  tack  some  canvas  between  the  cam- 
shaft floor  and  the  top  of  the  lower  guides,  giving  to  it 
a  decided  belly,  to  prevent  any  grease  thrown  by  the 
cams  from  falling  into  the  feeder  or  throat  of  mortar, 
or  on  the  plates.  In  one  mill,  where  very  poor  work 
had  been  done,  though  the  builder  and  superintendent 
claimed  most  thorough  knowledge,  we  found  boards 
placed  below  the  cams  to  prevent  the  grease  from  falling 
on  the  plates,  and  set  at  such  an  angle  that  there  was  a 
constant  rolling  of  pellets  of  grease  directly  into  the 
throat  of  the  mortar. 

We  now  come  to  the  concentrators,  and  it  can  be  safely 
stated,  with  hardly  an  exception,  that  the  cleanliness  of 
the  machines  is  a  sure  indication  of  the  quality  of  work 
done,  and  the  closeness  of  saving  accomplished. 

Where  rubber  belts  are  used,  the  oil  rots  them,  the 
sand  and  grit  get  into  the  bearings,  causing  bumping, 
inequality  of  the  plane  of  the  table,  and  a  little  grease 
getting  into  the  pulp  will  prevent  the  saving  of  the  finest 
and  richest  of  the  sulphurets.  The  very  act  of  cleaning 
the  machines  brings  all  parts  under  close  scrutiny,  and 
many  a  serious  break-down  is  averted,  observed  in  time 
during  this  cleaning  at  regular  intervals.  Therefore,  be 
sure  and  watch  for  grease,  daily  caution  the  employes 
about  it,  spare  no  pains  nor  expense  to  have  every  part 


it; 


HINTS  ON  AMALGAMATION. 


Modern  Machinery. 

t'ia.  1. 
Copperplate.    2— Iron  strip.    3—  Wood  backing. 


HINTS  ON  AMALGAMATION.  17 

of  the  mill  at  all  times  as  if  on  parade,  and  the  close 
saving  and  freedom  from  break-downs  will  amply  repay 
all  the  trouble  and  outlay. 

Within  certain  limits  the  shape  of  the  mortar  does  not 
affect  the  economic  results  nearly  as  much  as  has  been 
supposed — that  depending  mostly  on  the  man  attending 
to  them.  A  mortar  must  be  narrow,  as  the  object  is 
to  get  the  ore  out  of  the  battery  as  fast  as  crushed.  The 
back  should  be  curved  from  the  throat,  so  as  to  throw 
the  ore  directly  on  the  center  of  the  "die."  This  back 
must  be  solid  metal,  and  on  no  account  have  copper 
plates  in  the  back.  Their  advantage  is  very  dubious, 
and  in  nine  cases  out  of  ten  their  use  is  a  very  great 
detriment  to  successful  work.  Without  them  the  copper 
plates  on  the  "chuck-blocks"  catch  as  much  amalgam  as 
both  combined;  there  is  less  surface  to  scour,  particular- 
ly with  low-grade  ore,  and  with  them  the  additional 
width  of  the  mortar  prevents  the  splash  being  exerted 
exclusively  against  the  screen,  and  reduces  the  crushing 
capacity  of  the  battery.  (See  Fig.  1.) 

The  discharge,  that  is,  the  distance  between  the  top 
of  die  and  bottom  of  screen,  should  be  within  a  fraction 
of  four  inches,  new  dies  requiring  wooden  strips  under 
the  screens  to  keep  this  height.  The  "drop"  of  the 
stamps  should  be  4y2  to  5  inches,  and  the  speed  always 
above  95  drops  per  minute,  preferably  above  100  drops. 
A  slow  drop,  besides  decreasing  the  duty  of  the  stamps, 
allows  the  quicksilver  to  settle  and  diminishes  its  com- 
minution so  that  too  much  is  liable  to  be  used  at  one 
time,  a  sure  loss  if  the  gold  is  floured.  A  quick,  short 
drop  more  nearly  approaches  the  action  of  the  pan  in 
pan  amalgamation,  keeping  all  the  pulp  in  constant 
agitation,  and  mixing  the  quicksilver  uniformly,  so  that 
all  parts  of  the  ore  come  in  contact  with  it  before  leaving 
the  battery. 


18  HINTS  ON  AMALGAMATION. 

The  "chuck-block,"  covered  with  the  copper  plate, 
should  be  entirely  separated  from  the  strip  of  wood  on 
which  the  screen  rests.  The  plate  should  touch  the  bot- 
tom of  the  screen  itself,  at  as  slight  an  angle  as  possible, 
and  should  be  very  nearly  vertical  and  five  inches  deep. 
Its  backing,  generally  of  wood,  must  be  as  slight  as 
possible,  so  as  to  place  it  far  from  the  dies.  It  is  held 


FIG  2. 


FIG.  3. 


Nodern  Machinery. 

FIG.  4. 

in  place  by  a  strip  of  iron,  which  extends  into  the  shoul- 
ders on  each  side  of  the  mortar. 

Two  chuck-blocks  should  be  made  with  the  blocks  to 
conform  to  the  height  of  the  screen  as  the  dies  wear 
down,  as  with  dies  half  worn  the  wooden  strip  under- 
neath the  screen  is  removed,  bringing  the  discharge 
down  to  normal  height,  and  the  copper  must  not  project 
above  the  bottom  of  the  screen-discharge. 

This  sketch,  made  without  a  scale,  as  the  width  of 
mortars  varies,  will  better  explain  it.  Figure  2  shows 
both  cross-section  and  longitudinal  section. 


HINTS  ON  AMALGAMATION.  19 

The  screens  (see  Fig.  3)  are  preferably  made  with  open- 
ings eight  inches  highland  the  entire  length  of  the  rnor- 
tar.  Abstain  from  putting  any  cross-pieces,  which  ob- 
struct the  freedom  of  discharge.  In  placing  the  screens 
the  chuck-block  is  first  put  in  place,  then  the  strip  of 
wood  on  which  the  screen  rests,  having  a  lining  of 
blanket  tacked  to  both  edges,  and  this  strip  of  wood 
is  keyed  by  the  shoulders  cast  on  the  lip  of  the  mortar. 
Then  the  screen  is  put  in  place  and  keyed  by  the  wedges 
driven  down  the  shoulders  on  each  side  of  mortar.  There 
still  remains  a  large  opening  between  the  top  of  screen 
and  the  bottom  of  the  upper  casting  of  the  mortar  itself. 
This  should  be  wide  enough,  even  with  new  dies,  to  al- 
low of  the  easy  insertion  of  the  arm  to  the  shoulder.  In 
most  mills  this  is  very  foolishly  closed  solidly  by  a 
wooden  false  screen  and  keyed  as  tightly  as  the  screen 
itself.  The  proper  way  is  to  take  a  strip  of  wood  the 
full  outside  width  of  the  mortar  in  length,  and  2x1 
inches,  and  on  this  tack  very  strongly  either  extra-heavy 
canvas  or  a  piece  of  rubber  belting,  which  just  fills  the 
opening  in  width  and  extends  a  little  below  the  upper 
edge  of  screen-frame,  in  depth.  The  advantages  of  this 
should  be  obvious,  but  a  few  of  them  may  be  named: 
First,  it  permits  the  inspection  of  the  interior  of  the  bat- 
tery at  all  times,  without  stopping  the  stamps;  second, 
the  cleaning,  twice  daily,  of  all  accumulated  chips  and 
other  clogging  of  the  inside  of  screen;  third,  the  exami- 
nation by  touch  of  the  amalgam  accumulating  on  chuck- 
block;  and,  fourth,  in  many  cases,  the  driving  on  and  re- 
placing of  shoes  without  removing  the  screen. 

The  greatest  advantage  of  all  is  that  the  mill  is  stop- 
ped as  little  as  possible,  and  hence  the  most  perfect 
amalgamation  maintained,  while  no  hard  amalgam  is 
broken  away,  as  always  occurs  when  the  screen  is  re- 


20  HINTS  ON  AMALGAMATION. 

moved.  In  fact,  as  my  first  great  point  was  "avoid 
grease,"  my  second  is,  "Never  remove  the  screen  of  a 
battery  till  the  run  is  ended,  if  it  can  possibly  be 
avoided,  and  the  finer  the  gold  the  more  important  this 
is." 

It  takes  a  very  appreciable  time,  after  a  battery  is 
started,  no  matter  how  short  the  stop  may  be,  before  all 
the  pulp  is  in  constant  agitation,  and  the  quicksilver 
mixed  with  it. 

This  rule  also  brings  us  to  the  proper  material  of 
which  to  have  the  screens  made,  and  in  this  as  well  as 
everything  else,  the  best  is  always  the  cheapest.  Theo- 
retically, wire  screens  expose  the  most  discharging  sur- 
face, but  they  clog  the  quickest,  and  have  to  be  removed 
to  be  cleaned  by  a  wire  brush,  a  very  serious  fault,  as 
stated  above.  Round-punched  holes  present  too  much 
dead  surface,  being  exactly  the  reverse  of  the  wire 
screens.  This  only  leaves  us  the  "burr-slot"  and  the 
"punched-slot,"  and  of  these  the  burr-slot,  though  clog- 
ging the  least  of  any,  wears  coarser  more  quickly  than 
the  punched-slot.  Therefore  the  advice  we  give  is  to 
use  in  stamp  batteries  "punched-slot  screens,"  of  the 
best  material  to  be  had.  Of  material  we  have  tinplate, 
Russia  iron  and  steel.  Tinplate  is  the  cheapest,  but  the 
screens  are  worn  out  within  a  few  days,  and  are  really 
the  most  expensive  in  the  results  that  can  possibly  be 
employed.  Russia  iron  will  not  break  easily,  but  the 
orifices  wear  so  coarse  within  48  hours,  particularly  on 
hard  quartz,  that  the  ore  will  not  be  pulverized  as  fine 
as  required.  This  leaves  us  only  the  steel,  which  breaks 
before  it  wears  coarse,  on  account  of  its  hardness.  Of 
course  there  is  steel  and  steel,  but  if  a  point  is  made 
about  it,  steel  screens  can  be  procured  which  will  not 
break  for  over  a  month  under  rough  usage,  and  even  in 


HINTS  ON  AMALGAMATION.  21 

that  time  the  size  of  the  apertures  has  not  appreciably 
increased,  i.  e.,  sufficiently  to  cause  any  loss  in  free  gold. 

Here  we  have  the  best  condition,  the  battery  in  steady 
operation  for  a  month,  the  pulp  in  steady  and  constant 
agitation,  no  disturbance  of  the  hard  amalgam,  by  re- 
moving a  screen;  and  the  greater  the  quantity  of  amal- 
gam in  the  battery,  the  more  of  the  fine  and  floured  gold 
is  caught  there.  Therefore  use  a  "steel,  punched-slot 
screen,"  of  the  size  found  by  experiment  to  be  the  best. 
Several  factors  determine  this  size. 

With  coarse  gold  this  is  not  of  so  much  moment,  but 
should  the  gold  be  fine,  it  is  necessary  to  crack  the  ore 
that  much  more  to  free  it.  This  degree  of  pulverizing 
depends  on  the  grade  of  the  ore,  as  in  many  cases  it  costs 
more  to  save  the  finest  gold  than  the  total  amount  saved, 
and  it  then  becomes  necessary  in  practical  reduction  to 
use  a  larger  sized  screen,  put  through  more  rock,  and 
pay  little  attention  to  additional  loss  in  the  tailings. 
However,  it  is  best  to  use  as  fine  a  screen  as  is  conform- 
able with  a  profit  in  working  the  mine. 

The  outside  of  the  screen  must  be  scraped  several 
times  a  day,  and  as  good  a  device  as  any  is  a  copper 
spade  with  the  edge  turned  over  at  an  angle  of  45  de- 
grees; wooden  handle,  copper  riveted,  as  shown  in 
Fig.  4. 

There  should  be  a  long  expanse  of  copper-plate  surfacs 
below  each  battery,  though  some  of  it  is  only  of  use  in 
case  of  faulty  amalgamation. 

These  plates  are  technically  divided  into: 

INSIDE  COPPER  CHUCK-BLOCK,  a  description  of 
which  has  already  been  given,  and  there  is  only  to  add 
that  it  is  an  unnecessary  expense  to  have  it  silver-plated. 

LIP-PLATE,  which  must  be  heavily  silvered,  at  least 
three  ounces  of  silver  to  the  square  foot  being  put  on  it. 


22  HINTS  ON  AMALGAMATION. 

This  plate  is  just  the  length  of  the  mortar  and  is  wide 
enough  to  extend  from  the  inside-edge  against  which 
the  bottom  of  screen  is  braced,  to  a  half-inch  beyond 
the  iron  lip  of  mortar.  Two  rectangular  holes  are  cut 
in  it,  to  allow  the  shoulders  of  lower  keys  to  project,  and 
the  wooden  strip  on  which  the  screen  rests  is  placed  on 
top  of  the  plate  and  holds  it  solidly  in  position. 

SPLASH  PLATE.— This  is  rarely  found,  even  in  the 


10"  "8" 


Modern  Machinery. 

best  mills,  but  is  of  the  utmost  importance;  the  more  so, 
as  the  gold  is  floured.  In  fact,  it  is  absolutely  necessary 
if  very  fine  gold  is  to  be  saved.  It  should  be  12  inches 
wide,  by  a  length  just  sufficient  to  fill  the  space  between 
the  shoulders  of  the  mortar.  There  are  several  ways  of 
adjusting,  but  in  every  one  the  point  to  be  observed  is, 


HINTS  ON  AMALGAMATION.  23 

that  it  shall  stand  in  front  of  the  screens  at  an  angle 
never  less  than  forty-five  degrees  and  better  if  over  fifty 
degrees  from  horizontal;  that  the  bottom  shall  be  at 
least  an  inch  below  the  bottom  of  the  screen,  and  the 
space  between  the  screen-frame  and  it  shall  not  exceed 
three-quarters  of  an  inch.  Take  this  plate  and  fasten 
it  to  an  inch  board,  leaving  a  margin  of  the  board  below 
the  copper  plate,  to  act  as  a  brace  to  the  stalactites 
slowly  formed,  and  then  by  back  supports,  stand  it  on 
the  edge  of  the  next  plates,  so  that  it  is  held  firmly 
against  the  mortar  and  yet  can  be  instantly  removed, 
as  shown  in  Fig.  5.. 

Another  way  of  great  simplicity,  which,  however,  has 
the  objection  of  causing  too  much  jar,  is  to  rivet  a  piece 
of  track  iron  on  each  shoulder,  at  the  angle  the  plate 
shall  stand,  and  slide  the  plate  down,  keeping  it  away 
from  the  screen  by  a  false  strip  tacked  to  the  front  of 
the  board,  along  each  side  of  the  plate  itself. 

By  studying  the  effect  of  this  its  advantages  can  easily 
be  seen.  Twenty  years  ago  it  was  universal  to  have 
a  spray  of  clear  water  constantly  dropping  on  the  apron- 
plate  to  form  a  slight  stoppage  of  the  pulp  and  cause  the 
amalgamated  gold  to  settle  and  attach  itself  to  the  plate, 
but,  as  future  working  of  the  pulp  was  very  much  hin- 
dered by  this  excess  of  water,  it  is  now  rarely  used. 
Again,  to  a  certain  extent,  the  output  of  the  mill  is  in- 
creased the  greater  the  amount  of  water  allowed  to  flow 
into  the  battery,  and  as  a  result,  all  the  water  that  could 
be  used  and  not  hinder  future  operations,  is  allowed  to 
run  into  the  mortars. 

No  matter  how  fine  the  gold  may  be,  if  it  is  free,  under 
proper  amalgamation,  it  will  adhere  to  an  amalgamated 
surface  if  brought  into  actual  contact  with  it,  and  this 
the  splash-plate  does  in  two  ways.  First,  half  of  the 


OF  THE 


24  HINTS  ON  AMALGAMATION. 

pulp  is  thrown  against  it  in  a  coarse  spray,  aiding  adhe- 
sion by  the  force;  second,  it  then  runs  down  the  plate, 
dropping  off  the  bottom  exactly  similar  to  the  spray  from 
the  clear  water  troughs  used  in  earlier  times,  forming 
a  dam  and  eddies,  which  cause  the  other  half  of  the  pulp 
to  precipitate  its  fine  amalgam  at  this  point. 

From  here,  the  object  to  be  attained  is  to  have  no  rap- 
id and  strong  currents.  To  turn  the  pulp  over  and  over, 
so  that  all  parts  are  frequently  brought  in  contact  with 
the  amalgamated  surface,  and  to  spread  this  pulp  as 
thin  as  consistent  with  keeping  it  in  constant  motion  and 
allowing  no  settling  of  even  the  heavy  sulphurets  on  the 
plates.  It  is  also  found  that  an  occasional  drop  of  one 
inch  to  one  and  one-half  inches  is  a  benefit. 

Now  we  come  to  one  of  the  greatest  mistakes  made  by 
90  per  cent,  of  all  amalgamators,  an  error  held  to  like 
the  grip  of  death  by  men  of  broad  technical  education, 
causing  the  failure  of  many  properties  which  should  be 
successful. 

This  is  the  grade  given  to  the  large  plates.  These 
should  never  be  placed  with  less  than  2y2  inches  to 
each  foot,  and  in  most  cases  3  inches  would  be  better, 
and  even  more,  while  better  work  can  be  done  at  an 
angle  of  forty-five  degrees  than  with  a  grade  less  than 
2%  inches. 

Take  a  case  where  the  plates  are  set  below  2y2  inches, 
we  find  an  excess  of  water  required  to  keep  all  the  pulp 
moving  and,  therefore,  too  great  a  depth,  so  that  the 
fine  gold  is  held  in  solution  and  never  touches  the  amal- 
gamated surface,  when  we  truly  have  float  gold,  while  an 
equally  bad  feature,  almost  universal,  is  that  it  allows 
too  much  quicksilver  to  be  used,  and  fine  gold  will  never 
be  saved  with  even  a  slight  excess  of  quicksilver.  This 
point  will  be  more  fully  explained  under  the  discussion 
of  amalgamation. 


HINTS  ON  AMALGAMATION.  25 

With  the  plates  at  the  proper  grade  and  the  requisite 
amount  of  water,  the  pulp  travels  down  the  plates  in 
a  succession  of  waves,  the  lower  edge  of  each  wave 
rolling  over  and  over  and  bringing  every  particle  of 
water  even,  in  contact  several  times  with  the  amalga- 
mated surface.  The  more  sulphides  the  ore  carries,  the 
steeper  must  be  the  grade  of  the  plates,  to  clear  them  and 
still  not  interfere  with  the  concentration  of  the  tailings. 

After  this  explanation  we  can  continue  the  descrip- 
tion of  the  plates. 

From  the  lip-plate  the  pulp  has  a  drop  of  nearly  two 
inches  and  falls  on  the  first  plate  separate  from  the  mor- 
tar. 

The  apron-plate  should  be  divided  into  two  sections, 
the  first  easily  removed  at  all  times.  This  should  be  the 
full  length  of  the  mortar,  and  two  feet  wide,  and  that 
end  nearest  the  battery  resting  on  the  wooden  shelf  fast- 
ened to  wooden  mortar-block,  and  held  in  place  by  the 
lip  of  the  mortar  or  a  strong  hook  on  each  side,  while  the 
lower  end  rests  on  the  second  section.  This  second  sec- 
tion must  have  the  same  width,  and  be  from  4  to  6  feet 
long.  It  is  supported  by  extension  legs  firmly  secured  to 
the  floor.  By  using  this  form  of  support  the  grade  of  the 
table  can  be  changed  to  suit  the  ore,  after  practical  ex- 
periment. Start  with  a  grade  of  '^  to  3  inches,  and,  if 
too  much  water  is  required  to  keep  all  the  pulp  in  steady 
motion,  lower  the  second  section  (the  first  assuming  the 
same  grade,  as  it  rests  on  it),  until  the  pulp  is  seen  to 
move  freely  and  in  successive  waves  with  a  minimum  of 
water. 

On  most  ores  this  amount  of  plate  surface  is  all  that  is 
necessary,  but  if  there  is  still  sufficient  fall  to  allow  the 
tailings  to  be  readily  carried  away  automatically,  the 
pulp  is  now  passed  over  "sluice  plates,"  as  a  safeguard 


26  HINTS  ON  AMALGAMATION. 

against  accidents,  after  passing  through  a  quicksilver 
trap.  -  |  *  i|i'J 

These  sluice  plates  are  18  inches  wide  and  from  8  to 
10  feet  long,  and  are  set  at  a  minimum  angle  of  1%  inch 
per  foot.  All  the  plates  should  have  a  coating  of  silver 
of  three  ounces  to  every  square  foot,  although  on  the 
sluice  plates  two  ounces  will  do. 

There  are  several  devices  for  traps,  but  most  of  them 
are  only  receptacles  where  a  slight  obstruction  to  the  flow 
of  the  current  is  given  and  this  is  not  enough.  We 
want  to  accomplish  two  objects:  first,  retain  all  the 
amalgam  and  quicksilver  that  may  have  escaped  the 
copper  plates;  second,  secure  this  with  a  minimum  of 
sand  and  sulphurets. 

A  large  open  box  is  always  filled  with  sand  which  is 
gradually  replaced  by  coarser  sand  and  sulphurets  ac- 
cording to  the  length  of  time  before  its  complete  re- 
moval, while  only  a  modicum  of  loss  is  arrested  here. 
The  next  result  of  experimenting  caused  the  pulp  to  de- 
scend on  one  side  and  rise  on  the  other  of  a  partition, 
the  higher  specific  gravity  of  the  valuable  portions  aid- 
ing their  retention,  and  it  is  on  this  principle,  that  the 
most  successful  traps  are  now  constructed;  the  best  of 
all  being  those  used  in  the  mills  of  the  "Homestake"  in 
the  Black  Hills,  and  designated  as  the  "Black  Hills 
Trap." 

This  can  easily  be  constructed  of  wood  by  any  good 
carpenter,  as  it  consists  of  a  wooden  box  with  sheet 
iron  partitions,  loosely  set  in  grooves  cut  in  the  sides 
of  the  box.  A  trap  for  five  stamps  is  given  here.  It  is 
made  of  V/2  inch  clear  lumber;  inside  measure  horizon- 
tally 10  inches  wide  by  8  inches;  depth  at  inlet,  18 
inches;  at  outlet,  6  inches.  Plough  three  grooves  equally 
distant  in  each  side  and  *4  inch  deep,  making  them 


HINTS  ON  AMALGAMATION. 


27 


wide  enough  to  allow  a  sheet  of  heavy  iron  or  copper  to 
slide  readily  up  and  down.  The  middle  groove  should 
extend  clear  to  the  bottom  of  box  while  the  other  two 
are  stopped  2  inches  from  the  bottom. 

Fig.  6  shows  the  details  of  construction  of  box,  a 
perspective  view  and  the  method  of  attaching  handle 
to  the  middle  partition. 

The  first  iron  or  copper  plate  is  cut  10%  inches  wide 
and  18  inches  long,  with  a  handle  riveted  to  its  upper 


\ 


\ 


Modern  Machinery. 

edge.  The  second  is  cut  10%  inches  wide  and  12  inches 
long,  with  a  rod  riveted  at  each  side  and  extending  up 
4  inches,  as  shown  in  cut.  The  third  is  like  the  second, 
10%xl2  inches,  with  a  handle  riveted  on  its  upper  edge 
like  the  first. 

Here  we  have  at  two  separate  times  6  inches'  pressure 
to  force  the  pulp,  the  first  time  a  vertical  distance  of  12 
inches,  the  second  time  a  distance  of  6  inches,  both  prac- 
tically prohibiting  the  escape  of  a  metal  of  such  a 


HINTS  ON  AMALGAMATION. 


high  specific  gravity  as  quicksilver,  even  if  very  finely 
comminuted  and  still  not  enough  to  prevent  the  escape 
of  all  the  pulp  and  sulphurets  except  a  slight  layer  less 
than  two  inches,  which  also  is  in  constant  agitation  as 


f  £>ox 


Modern  Machinery. 

long  as  the  same  amount  of  water  is  employed.  Should 
this  water  get  slack  from  any  cause,  the  first  division 
at  once  becomes  choked,  but  the  trap  is  quickly  freed 


HINTS  ON  AMALGAMATION.  29 

by  raising  the  first  partition.  When  the  trap  is  cleaned 
all  the  partitions  are  withdrawn  and  the  residue,  very 
small  in  quantity,  is  removed. 

The  pulp,  on  leaving  the  apron-plate,  falls  into  a 
box  with  the  bottom  sloping  from  each  side  to  a  central 
vent,  from  which  it  flows  directly  into  the  trap,  and  on 
leaving  the  trap,  either  flows  over  the  sluice-plates,  or, 


Modern  Machinery. 

in  their  absence,  into  wooden  or  iron  launders,  to  be  con- 
veyed to  the  concentrators.  Fig.  7  shows  two  cross-sec- 
tions of  the  box  in  front  of  apron-plates. 

The  battery  tailings,  after  leaving  the  sluice-plates, 
or,  if  they  are  absent,  the  amalgam  trap,  fall  directly  into 
the  concentrating  launders.  These  are  preferably  made 
of  wood,  as  iron  pipes,  if  choked  by  broom  straws, 
pieces  of  blanket,  etc.,  have  to  be  disjointed  to  be  cleaned. 
These  wooden  boxes,  troughs  or  launders  measure  inside 
4  inches  wide  by  6  inches  high,  and  must  have  at  the 
very  least  a  grade  of  %  inch  per  running  foot.  Now, 
under  the  most  careful  management,  a  little  amalgam 
and  quicksilver  escapes  all  the  devices  mentioned  above, 
and  it  is  advisable  to  put  in  a  couple  of  "riffles"  in  each 
box  length  of  12  feet.  This  is  done  in  this  way:  Before 
the  bottom  piece  is  nailed  to  the  sides,  make  a  saw-cut  at 
right  angles  to  the  length  equally  distant  and  a  half  inch 
deep,  and  then  gouge  out  to  it  from  the  upper  side.  This 
is  shown  in  Fig.  8. 

If  the  water  used  is  always  the  same  in  quantity,  a 
V-shaped  box  will  carry  the  sand  with  the  smallest 


30 


HINTS  ON  AMALGAMATION. 


amount,  but  should  the  water  slacken  at  all  the  sand  at 
once  makes  a  broader  surface  and  then  from  the  in- 
creased friction  and  breadth  the  launder  is  at  once  filled 
to  the  top.  To  gain  some  advantage  from  the  V-shaped 
form  we  have  found  great  benefit  in  putting  angle  strips 


.  s 


Modern  Machinery. 

along  each  side  of  the  box,  1  inch  wide  and  1  inch  high, 
giving  a  2  inch  bottom  with  flaring  sides,  as  shown  in 
Pig.  9. 

When  the  pulp  is  divided  over  two  machines  a  division 
with  a  long  swinging  finger  is  put  in  and  each  launder 
reduced  to  a  width  of  2  inches,  from  the  end  of  which  it 
is  carried  by  a  rubber  hose  to  the  concentrators. 

THE  CONCENTRATORS.— As  stated  in  the  beginning, 
all  sulphurets  of  a  value  above  $50  per  ton  require  a 
shaking  table  with  an  endless  belt  that  must  work 
without  a  jar,  and  be  at  all  times  completely  under  the 
control  of  the  operator. 

Two  classes  of  machines  are  in  vogue,  one  shaking 
sidewise  or  across  the  stream,  the  other  with  an  end- 
shake  against  and  with  the  stream.  Years  of  practical 
experience  have  proved  that  the  end-shake  concentrators 
cannot  produce  concentrates  free  from  foreign  matter, 


HINTS  ON  AMALGAMATION.  31 

though  in  some  cases  the  tailings  have  a  very  low  valu- 
ation, while  any  attempt  to  make  clean  headings  results 
in  excessive  loss.  This  can  readily  be  seen  as  the  up- 
stroke against  the  current  exerts  too  great  a  force  against 
the  clear  water  regulated  for  the  downstroke,  while  if 
regulated  with  sufficient  force  to  keep  the  sand  back  on 
the  upstroke,  it  washes  down  the  finer  and  lighter  sul- 
phurets  during  the  downstroke.  This  has  been  acknowl- 
edged by  the  inventors  of  the  end-shake  machines,  from 
the  fact  of  the  universal  application  of  the  side-shake 
since  that  special  patent  has  expired. 

The  first  of  these  side-shake  machines  is  still  taken 
as  the  standard,  being  superior  in  the  estimation  of  the 
world  in  its  operation  and  ease  of  adjustment,  and  far 
ahead  in  the  quality  of  material  employed  in  its  con- 
struction. This  makes  it,  however,  the  most  expensive 
at  first  cost,  though  the  cheapest  in  the  end.  This  is 
known  as  the  "Frue  Vanner,"  and  the  general  applica- 
tion of  all  being  the  same,  it  will  be  taken  to  illustrate 
the  general  method  of  concentration.  However,  we  wish 
first  to  explain  the  reason  for  the  use  of  a  wooden  frame, 
to  which  some  objection  is  made.  It  is  this,  that  there 
is  sufficient  spring  to  a  wooden  frame  to  prevent  any  jar 
to  the  table  as  it  is  thrown  an  inch  each  way,  and  this 
jar  is  always  very  perceptible  on  all  the  machines  resting 
on  a  rigid  iron  frame. 

We  will  now  continue  the  course  of  the  battery  tail- 
ings. The  concentrator  is  set  with  a  grade  regulated  by 
screws  at  the  foot,  up  which  and  against  the  cur- 
rent the  endless  belt  travels,  and  this  grade  is  arranged 
so  that  there  is  at  all  times  a  thickness  of  pulp  of  ^ 
inch  which  is  neither  stiff  nor  sticky.  The  speed  of  the 
shaking  motion  for  average  ores  is  started  at  190  revo- 
lutions per  minute,  and  then  the  proper  grade  is  deter- 


32  HINTS  ON  AMALGAMATION. 

mined  only  after  actual  experiment.  The  pulp  falls  on 
the  machine  near  its  upper  end,  being  uniformly  distrib- 
uted by  the  "ore-spreader"  over  the  entire  width  of 
the  belt.  On  this  ore-spreader  it  is  well  to  have  a  silver- 
plated  copper  plate,  as  this  is  the  last  opportunity  to 
catch  separately  any  amalgam  or  quicksilver  that  may 
have  escaped  all  the  other  devices. 

The  ore-spreader  must  deliver  the  pulp  to  the  belt  with 
as  little  splash  as  possible  so  as  not  to  disturb  the  sul- 
phurets  that  have  already  settled.  To  do  this  there 
should  be  a  step  added,  as  shown  in  Fig.  10,  to  break 
the  fall,  and  this  step  must  just  clear  the  surface  of  the 
pulp  already  on  the  machine. 

In  front  of  this  ore-spreader  is  placed  a  clear  water 
distributer,  which  supplies  just  enough  water  to  sepa- 
rate the  remnants  of  sand  from  the  sulphurets,  and  take 
the  place  of  the  water  coming  down  with  the  pulp. 
The  water  should  be  just  enough  to  keep  all  the  field  be- 
tween the  water  distributor  and  the  ore-spreader  cov- 
ered with  water  without  a  current.  Too  little  water  is 
shown  by  a  series  of  dry  fingers  against  which  the  finest 
sulphurets  shake,  become  dry  and  float  down  the  ma- 
chine uncaught.  Should  some  sand  come  up  with  the 
sulphurets  and  no  dry  fingers  be  exposed,  do  not  turn  on 
more  water,  but  either  decrease  the  speed  of  the  uphill 
travel  of  the  belt  if  the  bed  of  pulp  is  the  right  depth 
and  not  sticky,  or  give  the  machine  a  steeper  grade  by 
lowering  the  foot.  The  tailings  from  the  concentrators 
under  proper  management  should  show  by  panning  tests 
no  more  sulphurets,  though  perhaps  an  assay  by  fire 
will  still  show  that  too  much  is  being  lost,  either  in  sul- 
phurets too  finely  slimed  to  be  collected  by  hand  tests 
or  in  tellurides,  oxidized  minerals  or  carbonates.  Very 
often  these  fine  slimes  can  be  saved  with  coarse  canvas, 


HINTS  ON  AMALGAMATION. 

Ore  >--^c/<?^ 


fig.  II 


r/g.i2 


.&",.. 


5- 

C- 

Modern  Machinery. 


84  HINTS  ON  AMALGAMATION. 

requiring  very  little  additional  expense  except  the  first 
outlay  in  erecting  the  plant.  We  can  safely  say  that  m 
ninety-nine  per  cent,  of  these  cases  all  the  value  is  in 
the  slimes,  so  that  our  first  duty  is  a  mechanical  separa- 
tion or  sizing.  This  separating  is  done  with  the  well- 
known  "spitz-kasten,"  a  V-shaped  box  divided  by  a  par- 
tition. Here  the  coarse  sand  is  drawn  out  through  a 
hole  at  the  point  of  the  V,  while  the  slimes  overflow  at 
the  top,  clear  water  being  added  to  help  the  separation. 
The  cross-section  in  Fig.  11  will  explain  the  principle. 

The  slimes  and  water  are  now  carried  in  launders  to 
the  canvas  plates,  always  made  in  duplicate  to  allow  the 
cleaning  of  one  set  while  the  slimes  are  flowing  over  the 
other.  The  cleaning  is  done  with  a  broom  and  in  some 
cases  a  spray  of  clear  water  under  pressure.  The  tables 
are  made  of  matched  lumber,  varying  from  4  feet  to  12 
feet  wide  and  10  feet  long.  They  are  set  at  a  grade  of 
1%  inches  for  each  running  foot,  and  are  covered  with 
No.  6  canvas.  As  stated  above,  the  tables  must  either  be 
made  in  duplicate  or,  in  a  large  plant,  a  couple  of  extra 
tables  are  provided,  to  be  used  while  cleaning  those  i-n 
steady  use.  The  slimes  and  water  flow  down  one  series 
of  tables  for  a  definite  time,  generally  one  to  three  hours, 
when  the  pulp  is  turned  off  and  a  small  amount  of  clear 
water  is  used  to  carry  off  a  little  of  the  waste.  Then  a 
tilting  board  is  placed  under  the  foot  of  the  table  and 
the  concentrates  swept  and  washed  into  the  settling 
box.  The  concentrates,  if  rich  enough,  are  shipped  with- 
out further  handling,  but  it  is  found  occasionally  to  be 
of  benefit  to  reconcentrate  them  over  a  machine  set  with 
very  little  grade,  and  running  at  a  very  low  speed.  We 
show  in  Fig.  12  the  method  of  saving  the  washings  of 
the  canvas  plates,  as  generally  adopted  In  California. 


CHAPTER  II. 
CARE  OF  QUICKSILVER, 

It  is  generally  acknowledged  that  special  care  must 
be  exercised  to  keep  the  quicksilver  absolutely  pure  and 
lively,  and  the  advice  given  is  to  retort  it,  as  that  will 
eliminate  all  the  impurities.  This  is  a  fallacy,  because 
there  are  certain  elements  which  will  vaporize  with 
the  quicksilver  and  still  contaminate  it,  so  that  even  after 
retorting  we  find  it  necessary  to  resort  to  chemical  agen- 
cies to  establish  its  highest  efficiency.  We  buy  a  flask 
of  quicksilver  from  the  producers,  and  generally  find 
it  absolutely  pure,  but  at  times  the  mass  will  separate 
into  globules  which  have  a  repellent  power,  one  on  the 
other.  This  is  probably  caused  from  the  use  of  lime 
in  the  retorting  of  metal  from  its  ore  of  cinnabar. 
Lime  has  a  peculiar  effect  on  quicksilver,  as  a  slight 
addition  to  sluggish  metal,  separated  into  globules 
will  not  only  liven  it  up  but  cause  the  globules  to 
join  together,  while  an  excess  will  increase  more  than 
fourfold  the  repellance  of  the  globules  toward  each 
other.  Therefore,  we  must  suppose  the  fresh  unused 
quicksilver  is  contaminated  by  too  much  lime.  Two 
chemicals  are  open  to  our  use,  both  of  which  will  destroy, 
pound  for  pound,  an  equal  amount  of  the  quicksilver, 
viz.,  a  strong  solution  of  cyanide  of  potassium,  or  a 
weak  one  of  nitric  acid.  Now,  nitric  acid  causes  fuming, 
and  renders  the  millman  susceptible  to  salivation,  so 
that  it  is  better  to  use  cyanide,  if  possible,  in  all  our 
operations  of  cleansing. 

35 


86  HINTS  ON  AMALGAMATION. 

When  the  practical  adaptation  of  the  solubility  of  gold 
in  cyanide  of  potassium  became  generally  known,  the 
majority  of  millmen,  and  more  especially  the  owners 
of  mines,  were  afraid  to  use  any  cyanide  in  their  opera- 
tions, as  they  believed  they  were  liable  to  lose  much  of 
the  fine  gold  in  the  ore,  dissolved  by  the  cyanide.  This 
is  a  very  erroneous  impression,  except  in  a  case  where 
cyanide  in  solution  was  mixed  with  the  ore  previous 
to  the  introduction  of  quicksilver.  In  other  words,  cy- 
anide of  potassium  has  the  greatest  affinity  for  grease 
and  copper,  and  will  also  dissolve  quicksilver,  if  present, 
without  affecting  the  gold  at  all.  This  enables  us  to 
use  this  chemical  in  conjunction  with  quicksilver  to 
great  advantage  in  all  our  operations.  Always,  then, 
before  using  any  of  the  quicksilver,  add  to  it  a  solution 
of  cyanide,  and  a  strong  solution  is  better  than  a  weak 
one;  in  fact,  we  have  used  a  saturated  solution  with 
benefit.  Some  of  the  quicksilver  is  poured  into  a  china 
bowl  and  the  surface  is  covered  at  least  to  a  depth  of 
one-half  inch  with  the  solution,  with  which  it  must 
always  be  kept  covered.  As  each  spoonful  of  quick- 
silver is  fed  into  the  batteries  it  is  thoroughly  brightened 
and  cleansed  in  passing  through  the  supernatant  liquid, 
and  is  in  the  best  condition  to  catch  the  gold.  After 
the  quicksilver  has  been  in  use  in  the  mill,  it  is  fre- 
quently spoiled  by  certain  elements  in  the  ore,  or  some 
accidental  fouling,  such  as  the  heating  of  a  journal  and 
the  consequent  flowing  of  babbit  metal  into  the  ore-bin. 
From  the  elements  in  the  ore,  we  find  lead,  tellurium, 
and  selenium.  The  worst  fouling,  however,  comes  from 
babbit  metal.  This  turns  the  quicksilver  black,  mak- 
ing it  slimy  and  frothy.  In  this  case  retorting  of  the 
quantity  contaminated  must  be  resorted  to,  but  a  partial 
help  can  be  had  by  using  sulhpnric  acid,  allowing  the 


HINTS  ON  AMALGAMATION.  37 

fuming  to  go  on  for  several  hours,  with  occasional  stir- 
ring. The  loss  is  very  great.  Should  the  ore  contain 
tellurium  or  selenium,  it  will  always  be  found  neces- 
sary to  purify  the  quicksilver  after  retorting,  as  these 
metals  are  carried  over  with  the  quicksilver  in  distill- 
ing the  quicksilver  from  the  amalgam.  Here  we  must 
employ  nitric  acid,  allowing  it  to  fume  for  several  hours. 
Then,  after  washing  thoroughly,  a  solution  of  cyanide  is 
added,  turning  the  liquid  black.  On  removing  this  with  a 
sponge,  the  quicksilver  is  found  to  be  in  perfect  condi- 
tion. Some  advise  the  addition  of  a  small  amount  of 
sodium  amalgam  to  the  quicksilver,  but  personally  we 
are  very  averse  to  using  it  on  account  of  its  causing  even 
the  iron  of  the  mortar  to  be  amalgamated,  while  the 
amalgam  on  the  plates  is  kept  too  soft. 

Turning  then  to  the  room  especially  set  apart  for 
chemicals  and  quicksilver,  and  specifically  known  as  the 
clean-up  room,  we  need  to  keep  in  stock  all  our  supplies, 
which  consist  of  the  following  list:  Commercial  cyanide 
of  potassium,  O.  P.  nitric  acid,  C.  P.  Sulpuhic  acid,  10 
pounds  of  copperas  or  sulphate  of  iron,  10  pqunds  of 
blue-stone  or  sulphate  of  copper,  some  pieces  of  soft 
chalk  for  lining  the  retort,  a  heavy  horseshoe  magnet, 
a  40-mesh  screen  18  inches  in  diameter  for  sieving  wood- 
ashes,  a  mortar,  and  pestle  of  one  quart  capacity  and 
one  of  two  quarts,  two  gold  pans  and  one  copper  bottom 
pan,  two  white  enameled  iron  pails,  two  porcelain  lined 
kettles  with  bales,  of  one  gallon  capacity  and  two  of 
half  gallon,  several  pint  and  quart  stoneware  bowls, 
and  several  cups  without  handles,  a  large  carriage 
sponge  and  several  smaller  sponges,  a  few  yards  of  fine 
canvas,  one-half  dozen  whisk  brooms  of  better  quality 
than  the  ordinary  clothes  brushes,  a  couple  of  scrubbing 
brushes,  one-half  dozen  hand  whitewash  brushes,  a 


HINTS  ON  AMALGAMATION. 


u 


Modern  Machinery. 


HINTS  ON  AMALGAMATION.  39 

couple  of  square  rubber  scrapers,  or,  what  is  better,  new 
rubber  belting  with  sharply  cut  edges,  having  at  least 
a  dozen  already  prepared,  and  a  small  platform  scale 
for  weighing  the  quicksilver  and  amalgam.  This  should 
use  avordupois  weights,  as  it  is  only  the  bullion  itself 
that  is  weighed  in  troy  ounces. 

Make  the  floor  of  matched  lumber,  on  top  of  the  reg- 
ular flooring,  with  a  tightly  fitted  baseboard  all  around 
the  room,  remembering  that  quicksilver  is  very  elusive 
and  disappears  from  no  apparent  cause.  This  room  is 
placed  to  one  side  of  the  battery  floor  with  one  win- 
dow that  commands  a  full  view  of  the  batteries  on 
one  side,  and  a  window  letting  in  light  from  the  outside, 
directly  in  front  of  the  clean-up  tank,  while  the  door, 
secured  by  a  padlock,  leads  from  inside  the  mill  and 
never  from  the  outside,  so  that  all  persons  before  get- 
ting to  this  important  room  must  pass  before  the  obser- 
vation of  the  mill  employees.  A  ground  plan  is  given  in 
Fig.  13. 

The  work-bench  is  made  of  2-inch  lumber,  with  solid 
legs  that  will  not  jar  the  room  when  heavy  hammering 
is  done.  On  this  old  screens  are  removed  from  their 
frames  and  new  ones  put  on,  and  as  there  is  always 
some  amalgam  attached  to  the  old  screens,  the  top  of 
the  table  must  be  tight  so  that  the  residue  can  be  col- 
lected and  planned.  The  implements  required,  each  of 
which  should  have  its  place  just  above  the  table,  are,  a 
light  hammer,  a  steel  scraper  (home  made,  either  from 
an  old  file  or  a  putty  knife),  a  tack  extractor,  a  pair  of 
snips  or  tin  shears,  and  a  punch  to  enable  the  tacks  to 
enter  the  steel.  The  only  tacks  of  any  account  are 
those  known  as  upholstery,  ordinary  carpet  tacks  in- 
variably losing  their  heads,  while  small  wire  nails  are 
held  too  firmly  by  the  wood  for  subsequent  withdrawal 


40  HINTS  ON  AMALGAMATION. 

on  replacing  the  screens.  The  punch  is  made  of  steel, 
similar  to  a  scratch-awl,  or  according  to  Fig.  14.  There 
must  also  be  here,  ready  to  hand,  a  piece  of  blanket  of 
good  quality  and  strips  of  wood  of  various  sizes,  for 
patching  a  hole  in  a  screen  temporarily,  when  it  is  not 
advisable  to  remove  it  just  th^n,  as,  for  instance,  during 
the  night  when  nearing  the  end  of  a  run,  with  so  much 
amalgam  inside  the  battery  that,  to  save  any  further 
dispute,  it  will  be  as  well  only  to  open  the  battery  in 
the  presence  of  the  party  who  is  directly  responsible.  A 
stock  of  screen  frames  with  ne\v  screens  on  and  ready 
for  use  must  always  be  kept  on  hand,  and  this  reserve 
should  never  be  less  than  three,  as  in  no  instance  is  the 
old  adage  so  exemplified  of  "time  being  money"  than 
the  moments  lost  in  stopping  a  battery  from  its  work. 
In  putting  the  new  screens  on  the  frame,  be  sure  that 
the  rough  side,  presenting  the  smallest  openings  is  on 
the  inside. 

The  cupboard  must  be  arranged  to  be  kept  under 
lock  and  key,  be  fitted  with  shelves  on  which  all  the 
supplies,  scrapers,  chemicals,  assortment  -of  wire  nails 
and  quicksilver  are  kept,  but  no  oil  or  grease  must  be 
allowed  in  this  room. 

In  arranging  the  tray  and  panning  tank,  we  must 
get  the  best  light  possible  on  our  work,  and  therefore 
they  must  be  placed  in  front  of  the  window  on  the  out- 
side of  the  building.  The  tank  must  be  4  feet  6  inches 
by  2  feet  on  top  and  tapering  to  the  bottom,  where  the 
dimensions  are  4  feet  by  18  inches.  It  must  be  2  feet  G 
inches  deep.  Six  inches  from  the  top  is  placed  an  over- 
flow pipe,  discharging  outside  the  building  into  a  sluice 
a  few  inches  wide,  either  set  with  riffles  or  covered  with 
a  copper  plate,  while  a  drain  hole,  stopped  with  a  plug, 
is  bored  just  above  the  bottom.  A  slat  is  tacked  along 


HINTS  ON  AMALGAMATION.  41 

each  side,  a  foot  from  the  top,  on  which  a  movable 
wooden  grate  can  Ibe  placed,  to  rest  a  pan  while  breaking 
up  the  lumps,  or  a  screen  that  requires  washing. 

On  the  left  side,  and  projecting  an  inch  over  the  tank, 
is  placed  the  tray  solidly  built  and  absolutely  Avater- 
tight.  This  should  be  4  feet  6  inches  long,  and  at  least 
18  inches  wide,  have  a  bottom  preferably  of  one  piece 
of  l^-inch  clear  lumber,  having  edgings  2  inches  high  on 
three  sides,  and  open  in  front  of  the  tank  with  a  gutter 
along  this  open  side  to  collect  any  quicksilver  that  may 
run  down.  The  slope  should  be  ^-inch  to  each  foot. 
Over  this  tray  must  be  placed  a  clear-water  pipe,  V2  or 
%-inch,  fitted  with  a  globe  valve  and  a  piece  of  rubber 
hose  12  to  18  inches  long.  This  is  explained  in  the  sketch 
of  Fig.  15. 

On  this  tray  the  chuck  blocks  are  scraped  and  all  the 
amalgam  put  through  its  final  cleaning.  The  scrapers 
are  made  from  old  files  of  all  lengths  and  shapes.  One 
edge  is  hammered  flat  and  ground  to  a  chisel  edge, 
while  the  other  end  is  bent  to  nearly  a  right-angle  before 
it  is  ground.  Shown  in  Fig.  16. 

The  brooms  are  improved  by  a  small  scraper  inserted 
in  the  handle,  as  shown  in  Fig  17. 

Be  sure  and  keep  a  large  stock  of  file  scrapers,  sharp- 
ened and  ready  for  use,  always  on  hand,  but  also  keep 
them  all  under  lock  and  key  till  wanted  in  cleaning  up. 

We  will  now  start  with  a  mill  newly  built  and  note 
the  final  preparations  necessary  before  the  run  is  begun. 
We  put  a  half  inch  of  dry  sand  in  the  mortars  and 
place  the  dies,  the  sand  being  required  to  act  as  a  cush- 
ion to  the  .blows  of  the  stamps  to  prevent  the  cracking 
of  either  the  mortar  itself  or  the  dies.  Then  the  shoes 
are  placed  on  top  of  the  dies,  the  shank  being  sur- 
rounded with  soft  pine  wedges  tied  on  with  a  string. 


42  HINTS  ON  AMALGAMATION. 

In  case  the  mill  is  a  very  large  one,  say  of  40  to  80 
stamps,  much  time  is  saved  by  preparing  this  circle  of 
wedges  beforehand.  It  is  done  in  this  way:  A  shoe  is 
taken  and  the  wedges  placed  around  it,  and  then  a 
strip  of  cloth  is  stretched  over  them  and  fastened  to 
each  wedge  with  a  tack.  This  circle  is  then  withdrawn 
and  a  sufficient  number  made  for  all  possible  use.  After 
that,  it  is  only  necessary  to  slip  one  of  these  circles 
over  the  shank  of  the  shoe,  and  it  is  at  once  ready. 
After  the  shoes  are  ready  they  are  driven  on  singly, 
by  the  power  employed,  a  board  being  placed  between 
the  shoe  and  the  die,  to  eliminate  any  danger  of  chipping 
the  iron.  They  are  then  hung  up  by  the  fingers  on  the 
cam  shaft  floor.  The  chuck-block  is  taken  to  the  clean- 
up room  and  amalgamated.  First,  it  is  thoroughly 
scoured  with  a  weak  solution  of  nitric  acid  till  the  true 
color  of  pure  copper  is  shown.  Then  washed  with  a  satu- 
rated solution  of  cyanide  of  potassium  and  quicksilver 
sprayed  from  a  bottle  over  the  mouth  of  which  a  piece  of 
canvas  has  been  stretched.  The  quicksilver  is  rubbed  into 
the  copper  by  the  exertion  mainly  of  "elbow  grease,"  as- 
sisted by  a  cloth  and  sand,  but  it  must  be  very  thor- 
oughly attached  to  the  copper,  the  surplus  being  re- 
moved by  one  of  the  "rubbers."  The  splash  plate  and 
lip  plate  are  also  dressed  in  the  clean-up  room  and  the 
operation  with  them  is  that  which  is  employed  on  all  the 
remainder  of  the  plates.  They  are  first  thoroughly 
scoured  with  cyanide  of  potassium  and  then  the  quick- 
silver is  sprayed  over  them  and  rubbed  hard  with  a 
cloth,  avoiding  all  the  use  of  sand  or  grit  of  any  kind. 
Cyanide  of  potassium  is  added  frequently  until  the  en- 
tire surface  looks  not  only  bright  but  wet.  Then  the 
surplus  quicksilver  is  again  squeezed  out  with  the  rub- 
bers and  the  plates  are  ready  for  use. 


HINTS  ON  AMALGAMATION.  43 

The  lip  plate  is  now  placed  in  position  and  the  chuck- 
block  keyed  to  its  place  and  the  first  section  of  the  apron 
plate  is  fastened  to  the  mortar  block.  Broken  ore,  both 
fine  and  coarse,  is  now  thrown  into  the  mortar  and 
packed  around  and  over  the  dies  to  a  depth  of  2  to  4 
inches,  when  the  screen  is  put  in  place  and  the  splash 
plate  attended  to  the  last  of  all.  The  water  is  now 
turned  on  from  two  cocks,  one  on  each  side  of  the  bat- 
tery and  directly  over  the  tops  of  the  stamp-heads.  Two 
streams  are  better  than  one,  as  it  enables  us  to  regulate 
the  proper  quantity  of  water,  and  also,  by  increasing 
the  amount  on  one  side  or  the  other  to  keep  the  duty  of 
each  stamp  uniform.  Until  this  water  has  reached  the 
bottom  of  the  trap  do  not  drop  a  stamp  and  then  only 
one  battery  of  five  at  a  time,  till  it  is  perfectly  under 
control,  both  in  regard  to  the  feed  of  ore  and  the  uni- 
form drop  of  the  stamps.  At  first  no  quicksilver  is 
added  on  account  of  the  excess  that  is  on  all  the  cop- 
pers, from  the  preliminary  amalgamation.  A  good  deal 
of  this  will  be  carried  away  by  the  attrition  of  the  sand 
and  the  jar  from  the  battery  within  an  hour,  when  we 
can  begin  to  regulate  the  proper  amount  and  interval 
of  time  to  feed  quicksilver.  On  average  ore  we  begin 
with  a  drop  the  size  of  No.  4  bird  shot,  and  as  the  out- 
side plates  gradually  get  drier,  gradually  increase  the 
amount  fed  each  time  till  we  find  the  plates  to  keep 
the  proper  color.  All  our  determinations  are  made  on 
the  splash  plate,  lip  plate  and  the  first  few  inches  of  the 
apron  plate. 

It  is  very  hard  to  put  on  paper  the  proper  color  ana 
consistency  of  amalgam  on  the  plates,  but  we  will  do 
the  best  we  know  how.  The  amalgam  on  the  splash 
plate  and  lip  plate  must  be  kept  hard  and  dry  or  very 
little  amalgam  will  remain  there.  The  first  four  inches 


44  HINTS  ON  AMALGAMATION. 

of  the  apron  plate  must  also  be  dry,  hard  and  immov- 
able to  pressure  by  the  finger,  while  below  it  gradually 
should  become  softer,  and,  when  pushed  by  the  finger, 
have  the  consistency  of  putty;  while  at  the  very  bottom 
of  the  apron  a  similarity  to  thick  molasses  is  not  too 
soft.  The  color  of  all  must  not  be  dull,  like  frosted  sil- 
ver, nor  as  bright  as  quicksilver  alone,  but  nearly  ap- 
proaches the  appearance  of  a  looking  glass.  Of  the  two 
extremes,  however,  the  dull  frosted  appearance  is  far 
preferable,  as  quicksilver  is  always  being  carried  by  the 
attrition  of  the  sand  and  where  quicksilver  goes  there 
is  lost  also  the  fine  gold  held  in  solution.  The  finer  the 
gold,  the  drier  must  be  kept  the  plates,  the  less  quick- 
silver put  in  at  one  time  and  the  shorter  the  interval 
between  the  additions  of  the  feed  into  the  mortars.  If 
too  much  quicksilver  is  added  it  is  at  once  noticed  from 
the  small  amount  collected  near  the  battery,  and  its 
accumulation  increasing  as  it  travels  down  the  plates. 
When  the  plates  are  kept  in  proper  shape  near  the  battery 
the  proper  wetness  can  be  controlled  at  all  times,  on  the 
lower  part  of  the  apron,  by  an  occasional  sprinkling  of 
quicksilver,  and  this  will  attract  the  last  of  the  flour 
gold  that  may  have  escaped  previous  amalgamation 
without  jeopardizing  the  gold  already  amalgamated  and 
collected  in  and  near  the  battery. 

Even  to-day  some  people  advocate  only  outside  amal- 
gamation, putting  no  quicksilver  at  all  into  the  battery, 
but  we  believe  that  as  much  gold  should  be  caught  in- 
side the  battery  as  possible  and  for  flour  gold  especially 
the  highest  efficiency  is  attained  with  dry  amalgama- 
tion in  the  battery  and  a  soft  but  not  wet  amalgamation 
on  the  lower  apron  plate  and  the  sluice  plates.  Even  on 
ore  that  runs  nearly  the  same  in  value,  day  in  and  day 
out,  constant  watchfulness  and  observation  of  the  condi- 


HINTS  ON  AMALGAMATION.  45 

tion  of  the  plates  must  be  exercised  and  it  is  generally 
advisable  to  examine  each  plate  with  the  aid  of  a  very 
small  stream  of  clear  water  each  time  any  quicksilver 
is  to  be  added.  Sometimes  a  touch  of  the  finger  is  suf- 
ficient to  inform  the  adept,  but  this  takes  a  long  time  to 
acquire,  so  as  to  place  any  trust  in  it.  In  addition  to 
observation  of  the  outside  plates,  daily  feel  the  chuck- 
block,  by  removing  the  canvas  over  the  screen  and  in- 
serting the  arm  very  carefully.  As  each  watch  of  men 
will  remove  the  chips,  etc.,  before  quitting  time,  of 
course  without  stopping  the  mill,  they  can  then  feel  the 
chuck-block,  see  that  everything  is  fastened  properly, 
that  the  amalgam  is  accumulating,  and  has  the  proper 
touch  and  hardness.  The  touch  of  amalgam  should  not 
be  slippery,  neither  should  it  be  sandy.  It  must  show 
a  uniform  hard,  dry,  and  solid  surface  on  the  chuck- 
block,  splash  and  lip  plates,  but  can  be  moved  into  a 
pasty  ridge  on  the  apron  plate.  In  regard  to  the  interval 
of  time  to  allow  between  the  feeding  of  the  quicksilver 
several  factors  must  be  considered.  All  gold  is  only 
amalgamated  on  its  surface,  and,  therefore,  coarse  gold 
requires  less  quicksilver  per  value  than  fine  gold,  which 
presents  a  larger  area  per  unit  of  value,  and,  in  addition 
to  this,  the  finer  the  gold  the  more  frequently  the  quick- 
silver must  be  -added.  If  it  is  found  that  the  size  of  the 
grains  of  gold  in  the  ore  have  diminished  rather  than  add 
the  necessary  addition  to  the  regular  dose  reduce  the 
interval  of  time  one-half,  or  as  found  most  beneficial. 

We  generally  expect  011  average  ore,  i.  e.,  $8  to  $10 
of  moderate  coarseness,  to  feed  quicksilver  once  every 
hour,  but  if  very  fine  and  floured,  once  every  half-hour 
is  not  too  often.  The  superintendent  must  allow  some 
discretion  to  his  amalgamators,  as  even  on  ore  of  very 
uniform  quality  it  is  not  politic  to  give  an  order  for  a 


46  HINTS  ON  AMALGAMATION. 

certain  feed  of  quicksilver  for  more  than  two  hours, 
and,  therefore,  it  is  very  necessary  that  thoroughly  com- 
petent men  alone  be  employed  in  this  capacity. 

We  feed  the  quicksilver  and  know  it  is  in  its  best 
condition,  but  our* labor  is  lost  unless  we  keep  it  in  that 
condition  as  far  as  possible  all  the  time.  Our  watchful- 
ness has  prevented  its  contamination  by  grease  and  yet, 
in  many  cases,  even  after  only  a  few  hours'  run,  we 
find  the  plates  coated  with  various  colors  that  would 
sicken  any  subsequent  amalgam  or  quicksilver,  so  that 
it  will  not  be  attached,  but  flows  on  to  waste.  This 
coating  must  be  removed,  even  if  thie  mill  is  stopped 
every  three  hours  to  "dress  the  plates." 

If  the  amalgam  is  removed  from  the  plates  too  fre- 
quently or  too  close,  the  silver  coating  disappears  very 
rapidly  and  just  as  soon  as  the  copper  is  exposed  the 
plates  are  always  tarnished  with  verdigris,  the  colors 
starting  as  a  pale  golden  yellow,  but  rapidly  becoming- 
dark,  greenish  and  brown.  For  this  there  are  only  two 
remedies,  one  to  remove  the  plate  and  have  it  re-sil- 
vered, and  the  other,  which  we  consider  far  better,  to 
amalgamate  it  with  gold  amalgam  and  be  more  careful 
in  the  future  from  removing 'the  amalgam  so  thoroughly. 
First,  clean  and  scour  till  the  pure  color  of  copper  is 
shown  with  cyanide  of  potassium,  or  a  solution  given 
later.  Then  amalgamate  with  quicksilver,  rubbing  it  in 
thoroughly  and  then,  after  removing  the  surplus  quick- 
silver, take  a  little  amalgam  of  floured  go^u  and  coat  the 
plate  thoroughly  with  it.-  Afterward  both  in  dressing  the 
plates  and  cleaning  up,  push  the  amalgam  from  other 
parts  of  the  plate  to  this  spot  until  it  is  found  to  keep  as 
bright  as  all  other  parts. 

With  the  ores  of  this  State,  California,  we  find  a  pur- 
plish brown  stain,  caused  by  telluride  of  gold,  a  black 


HINTS  ON  AMALGAMATION.  47 

or  very  dark  brown,  from  selenide  of  gold,  and  a  most 
beautiful  steel-blue  sheen  which  comes  from  iridosmium. 
These  stains  themselves  are  all  rich  in  gold,  and  unless 
saved  at  the  time  and  place  noted,  will  ^e  mainly  lost, 
as  they  defy  concentration,  are  apparently  soluble  in 
water  and,  without  special  chemical  treatment,  are  im- 
pervious to  the  action  of  cyanide  of  potassium.  It  is, 
therefore,  useless  for  us  to  use  simple  cyanide,  which, 
though  making  the  plates  and  quicksilver  bright,  would 
allow  all  this  scum  to  flow  to  waste. 

There  is  one  mixture,  however,  that  helps  us  very  ma- 
terially, known  to  very  few,  as  far  as  we  are  informed, 
and  only  employed  by  the  two  or  three  possessing  its 
simple  formula.  Even  where  there  is  no  special  need  for 
its  employment  we  always  use  it  in  preference  to  a  sim- 
ple solution  of  cyanide.  It  only  consists  of  a  mixture  of 
copperas  and  cyanide,  forming  a  solution  of  both  ferro 
and  ferri  cyanide  of  potassium. 

The  preparation  of  this  mixture  has  never  been  put 
in  an  exact  formula,  and  can  either  be  made  freshly 
each  day  or  in  quantity.  Our  method  has  been  to  take 
two  quarts  of  water  and  add  to  it  two  to  four  ounces  of 
cyanide  of  potassium,  and  when  this  has  partially  dis- 
solved, we  add  a  pint  of  a  saturated  solution  of  copperas 
and  stir  the  mixture  thoroughly;  but  on  using  this  mix- 
ture or  part  of  it,  we  do  not  clean  out  the  sediment  until 
necssary,  but  add  at  first  fresh  water  and  the  next  day 
more  of  the  different  ingredients  and  fresh  water  as 
needed.  Crude,  but  satisfactory  results  are  obtained. 
The  method  of  application  is  the  same  for  the  daily 
dressing  of  the  plates  as  well  as  to  remove  stains.  The 
stamps  of  one  battery  are  hung  up,  then  the  water  is 
turned  off  and  the  concentrators  attached  to  that  bat- 
tery are  stopped,  so  as  to  keep  their  load  uniform  and 


48  HINTS  ON  AMALGAMATION. 

lose  as  little  of  the  sulphurets  as  possible.  A  stream 
of  clear  water  of  considerable  strength  is  now  directed 
first  on  the  screens  and  then  over  the  plates  till  all  the 
sand  and  slimes  are  removed. 

Starting  at  the  bottom  of  the  first  section  of  the  apron 
plate  a  whisk  broom  is  dipped  into  the  mixture  and  the 
plate  rubbed  with  a  circular  motion,  of  which  the 
strongest  movement  is  upwards  towards  the  battery 
and  carries  the  amalgam  that  way.  This  is  repeated 
until  the  entire  section  has  been  scrubbed  with  the  mix- 
ture and  the  whisk  broom.  The  splash  plate  is  then 
tilted  over  and  the  mixture  brushed  lightly  over  it,  and 
afterwards  the  broom  is  drawn  lightly  over  the  lip 
plate,  but  any  amalgam  disengaged  is  brushed  to  the 
apron  plate.  Very  little  of  the  mixture  has  left  the 
plates  and  has  been  acting  on  the  gold  bearing  stains 
and  the  sulphurets  which  have  been  attached  to  the 
plates  by  the  particles  of  gold  mechanically  adhering  to 
them.  The  plates  are  now  brushed  up  in  a  straight 
line,  and  all  the  loose  amalgam  sulphurets,  etc.,  are  col- 
lected into  a  small  heap,  when  they  are  taken  up  with  a 
rubber  and  small  iron  scoop  and  put  into  a  china  bowl 
which  has  some  clear  water  in  it.  If  the  lower  apron 
is  also  stained,  it  is  treated  in  the  same  way,  but  gen- 
erally the  stains  are  kept  on  the  upper  plates.  Careful- 
ness has  been  taken  to  disturb  and  remove  as  little  of 
the  amalgam  as  possible,  and  most  of  it  is  saved  in  the 
china  bowl;  but  every  time  the  broom  is  dipped  into 
the  mixture  a  little  amalgam  is  washed  off  into  the 
kettle;  so  that  it  must  all  be  saved  and  once  a  week  or 
so,  poured  out  and  cleaned.  The  amalgam  now  lies  on 
the  plates  with  microscopic  ridges  caused  by  the  broom, 
parallel  with  the  current,  and  to  change  rhese  to  trans- 
verse ridges,  the  whitewash  brush  is  taken  and  drawn 


HINTS  ON  AMALGAMATION.  49 

continuously  across  the  plates,  back  and  forth,  till  the 
battery  is  reached,  when  the  water  in  the  battery  is 
turned  on,  the  stamps  are  dropped  and  the  concentrators 
started.  Generally  this  treatment  is  sufficient  when 
done  at  7  a.  m.  and  5  p.  m.  each  day,  but  as  stated 
above,  should  the  plates  again  become  stained,  hang 
up  and  dress  them  in  this  same  way,  even  as  often  as 
every  three  hours.  On  no  account  try  to  remove  the 
stains  with  the  battery  running  and  the  sand  passing 
over  the  plates,  as  much  amalgam  is  carried  away  and 
the  gold  in  the  stains  lost  forever.  Should  the  plates 
require  dressing  every  three  hours,  it  is  not  necessary 
to  rub  them  so  hard  with  the  whisk  broom,  except  in 
the  morning  and  evening,  but  this  double  dressing  must 
not  be  neglected,  even  if  the  plates  are  apparently  clean 
and  bright.  They  always  are  improved  by  it,  and  with 
practice  ten  to  fifteen  minutes  is  all  that  is  required 
on  each  battery.  Whenever  it  is  found  that  considerable 
4  amalgam  is  collecting  at  the  lower  part  of  the  plates, 
brush  it  up  with  the  broom  towards  the  head  of  the 
plates,  and  once  a  week  lightly  remove  the  surplus  from 
the  lower  apron  and  the  sluice  plates  with  a  rubber, 
but  do  not  touch  the  amalgam  on  the  splash,  lip  and 
upper  apron  till  the  time  for  the  general  clean  up  of  the 
mill,  as  the  thicker  the  amalgam  that  is  there,  the  more 
of  the  fine  gold  is  caught  and  nearer  to  the  battery  as 
well.  It  is  also  a  fact  that  gold  amalgam  is  less  liable 
to  tarnish  than  any  other  amalgam. 

We  occasionally  find  another  difficulty  to  contend 
with,  in  that  the  gold  is  "rusty,"  that  is,  coated  with  a 
film  rendering  its  surface  impervious  to  the  attack  of 
quicksilver.  This  is  of  rarer  occurrence  than  imagined, 
as  the  loss  of  gold  is  very  often  laid  to  this  cause,  when 
the  gold  is  capable  of  being  amalgamated  if  proper  care 


50  HINTS  ON  AMALGAMATION. 

and  knowledge  are  employed.  In  some  oxidized  ores, 
taken  above  water  level,  a  laboratory  test  of  amalga- 
mating will  show  gold  not  touched  by  quicksilver,  but 
here  the  ore  is  first  ground  by  itself  and  then  the  quick- 
silver and  water  (and  a  good  deal  of  water)  are  added 
and  it  is  shaken  in  a  bottle  or  stirred  in  a  wedgwood 
mortar,  after  which  the  amalgam  is  separated  by  pan- 
ning. In  a  battery  with  stamping,  coarse  gold  is  hit 
and  cracked  and  an  inside  bright  surface  exposed, 
which  is  at  once  attacked  by  the  quicksilver,  present  at 
the  same  time,  before  it  can  again  become  tarnished; 
while  fine  gold  is  ground  temporarily  bright  by  the  vio- 
lent agitation  of  coarse  and  fine  rock  thrown  against 
the  sides  of  the  mortar  and  the  screen  surface.  In  this 
way  a  great  deal  of  gold,  reported  as  rusty,  and  not 
available  for  amalgamating,  is  found  to  act  very  satis- 
factorily when  actually  worked,  while  this  result  is 
helped  by  the  use  of  our  sovereign  mixture,  the  high 
specific  gravity  of  gold  causing  it  to  remain  on  the 
plates  mechanically,  when  it  is  taken  up  for  future 
treatment  in  our  daily  dressing  of  the  plates.  If  we 
know  positively  that  we  are  dealing  with  rusty  gold, 
we  can  help  ourselves  a  little  by  throwing  into  the  bat- 
tery every  hour  a  piece  of  bluestone  the  size  of  a  wal- 
nut, but  our  principal  work  should  be  on  the  outside 
plates.  It  is  not  a  very  good  plan  to  put  any  cyanide  into 
the  battery,  as  it  may  dissolve  free  gold  before  the 
quicksilver  has  coated  its  surface  or  dissolved  it. 

After  the  dressing  of  the  plates,  the  kettle,  brooms, 
rubbers,  and  bowl  of  amalgam  and  dirt,  are  taken  to 
the  clean-up  room;  the  rubbers  and  brooms  are  washed, 
and  then  put  away.  If  the  mill  is  a  small  one,  ten 
stamps  or  less,  the  amalgam  collected  at  one  time  is  so 
small,  it  is  better  to  put  the  bowl  away  as  it  is,  and  only 


HINTS  ON  AMALGAMATION.  51 

clean  the  amalgam  when  sufficient  has  accumulated 
to  warrant  the  time  expended,  remembering  that  the 
chemical  mixture  is  acting  beneficially  and  more  of  the 
gold  is  in  condition  to  be  recovered.  If  the  mill,  how- 
ever, is  20  stamps  or  more,  enough  "muck"  (it  looks 
like  slimy  .mud,)  is  daily  collected  to  make  an  appre- 
ciable quantity  of  clean  amalgam,  and  this  daily  amount 
requires  closer  manipulation  than  the  large  quantity 
collected  on  clean-up  day.  When  we  find  we  have 
enough,  including  that  collected  from  replacing  the 
screens  or  any  other  source,  we  proceed  in  this  way: 
First,  we  have  a  bowl  of  quicksilver,  kept  specially  for 
this  purpose  and  used  over  and  over,  because  after  the 
first  cleaning  it  has  become  charged  with  all  the  gold 
it  will  carry  in  solution,  and  we  then  lose  no  more 
from  each  subsequent  daily  bath  of  the  new  amalgam. 
The  collections  from  the  plates,  sulphurets  and  all,  are 
dumped  into  this  quicksilver  and  thoroughly  mixed  with 
the  hand.  The  dross  rises  to  the  top,  though  a  little 
collects  around  the  sides  of  the  bowl  and  is  mechanically 
held  on  the  bottom.  Placing  the  bowl  in  a  gold-pan 
holding  some  water,  we  remove  the  dross  and  water 
with  a  small  sponge.  After  the  surface  is  cleansed,  the 
sponge  is  pressed  to  the  bottom  and  sides  and  all  the 
dross  possible  brought  to  the  surface  and  removed,  until 
the  quicksilver  is  bright  and  absolutely  dry.  This 
quicksilver  is  then  poured  slowly  into  another  bowl 
half  full  of  clear  water,  when  most  of  the  remaining 
dross  will  be  left  attached  to  the  sides  of  the  first  bowl, 
and  the  balance  will  be  floated  on  the  second  bowl  from 
which  it  is  removed  with  a  sponge.  The  dross,  with 
some  amalgam,  rusty  gold  and  quicksilver,  is  now  en- 
tirely in  the  gold  pan,  ready  for  further  treatment.  This 
is  now  put  into  one  of  the  iron  mortars  and  only  a  very 


52  HINTS  ON  AMALGAMATION. 

little  water  kept,  not  more  than  a  couple  of  tablespoons 
full,  as  we  require  the  mixture  to  be  thick  for  proper 
grinding.  It  is  now  ground  for  several  minutes,  in  fact, 
till  it  seems  to  be  nothing  but  a  slime,  when  the  mortar 
is  placed  in  a  gold  pan,  and  a  stream  of  clear  water 
under  pressure  is  turned  on,  the  mixture  being  rapidly 
stirred  with  the  pestle,  till  the  water  flows  clear,  over 
the  sides  of  the  mortar.  The  surplus  water,  except  a 
very  little,  is  then  poured  off,  and  the  grinding  renewed 
until  this  clear  water  is  dark  and  possibly  has  become 
thick  once  more,  when  the  operation  of  washing  with 
clear  water  is  again  employed.  After  this  second  wash- 
ing there  should  only  remain  with  the  amalgam,  the 
iron  from  the  battery  and  a  little  coarse  sulphurets. 
Leaving  the  water  in  the  mortar  the  iron  is  removed 
with  the  horse-shoe  magnet  and  then  the  water  re- 
moved, when  the  amalgam  collected  can  be  carefully 
added  to  that  in  the  bowl,  leaving  the  sulphurets  behind 
in  the  mortar.  If  this  last  amalgam  still  has  a  bluish 
or  brownish  coating,  it  is  a  gold-bearing  stain  and 
should  be  added  to  the  general  amalgam.  The  dross, 
sulphurets,  etc.,  are  now  put  into  the  copper-bottom 
pan,  which  has  been  amalgamated,  shaken  in  this  and 
washed  into  the  tank. 

A  piece  of  the  fine  canvas  is  taken  and  thoroughly 
wet  on  both  sides  and  then  placed  in  a  bowl  of  clear 
water.  Into  this  some  of  the  quicksilver  and  amalgam 
is  poured,  but  only  a  quantity  that  can  be  handled  con- 
veniently, the  canvas  is  twisted  tightly  and  the  quick- 
silver squeezed  through,  adding  the  amount  to  it,  until 
either  it  is  all  in  one  ball  or  the  ball  is  of  a  size  not  to 
be  cumbersome.  Now,  it  is  not  necessary  to  exert  great 
strength  to  eliminate  the  last  of  the  quicksilver,  as  more 
can  be  extracted  by  rubbing  the  hand  or  the  thumb, 


HINTS  ON  AMALGAMATION.  53 

with  a  steady  pressure  over  the  ball,  with  frequent 
immersions  in  the  water,  than  by  violent  twisting. 
When  the  amalgam  is  squeezed  dry  the  canvas  is  laid 
open  on  the  gold-pan,  the  bottom  covered  with  water, 
the  ball  of  amalgam  pressed  into  solid  shape,  all  de- 
tached pieces  added,  and  the  ball  is  then  rolled  over 
every  part  of  the  canvas.  In  that  way  it  collects  every 
speck  of  amalgam,  and  has  its  surface  smoothed  with 
the  small  amount  of  quicksilver  remaining  in  the  in- 
terstices of  the  canvas,  while  any  dirt  or  sulphurets  is 
kept  from  being  attached,  owing  to  the  water  in  the 
pan.  Dry  amalgam,  even  with  a  little  free  quicksilver, 
becomes  very  hard  in  24  hours,  and  the  slight  addition 
of  mercury  to  the  surface  of  the  ball,  from  rolling  over 
the  canvas,  acts  as  a  cement  to  keep  the  ball  together 
in  a  compact  mass.  The  canvas  is  washed  in  the  pan, 
squeezed  dry  and  hung  up.  The  floured  quicksilver  is 
collected,  rubbed  by  the  finger  into  a  globule  and  added 
to  that  in  the  bowl.  The  ball  is  now  weighed  in  avoir- 
dupois ounces,  and  put  into  the  safe  or  strong  box,  and 
entered  into  the  book  for  mill  reports,  as  the  product  for 
one  day  or  number  of  days,  as  the  case  may  be. 

It  may  seem  that  this  work  is  not  required  and  that 
the  amalgam  can  be  saved  and  cleaned  with  that  col- 
lected from  the  general  clean-up,  but  it  will  be  found 
to  be  money  saved,  to  attend  closely  to  the  instructions 
given  above,  and  particularly  where  we  have  to  contend 
with  tellurides.  The  foreman  of  the  mill,  or  the  super- 
intendent of  a  small  plant,  have  ample  time  each  day 
to  devote  to  this  work;  more  gold  will  be  acquired,  and 
the  retort  metal  alone,  in  its  cleanliness  and  the  small 
loss  from  the  subsequent  melting,  will  more  than  repay 
the  attention  to  the  small  details  advocated.  If  this  im- 
perfectly amalgamated  muck  is  roughly  panned  and 


54  HINTS  ON  AMALGAMATION. 

the  amalgam  alone  saved,  the  loss  in  a  month  is  ap- 
preciable, and  it  is  forever  gone,  while  this  is  the  only 
alloy  of  gold  which  is  hard  to  clean,  and  not  that  from 
the  chuck-blocks  or  inside  the  battery. 

We  see  the  mint  saving  the  dust  on  the  roof,  the  car- 
pets, and  the  clothes  of  the  workmen,  and  getting  a  mar- 
velous quantity  of  gold,  and  yet,  in  a  mill,  the  amal- 
gam, the  scrapings  and  refuse  are  all  handled  as  if  of 
no  more  value  than  the  sand  on  the  ocean  beach.  Lately 
a  report  was  made  by  a  responsible  consulting  mining 
engineer,  that  he  estimated  the  value  of  an  old  mill 
and  the  ground  on  which  it  stood,  to  be  over  $40,000.00 
in  amalgam,  quicksilver  and  sulphurets,  and  it  has  been 
our  experience  that  in  the  majority  of  mills  which  have 
been  in  operation  for  several  years  astonishing  results 
are  obtained  from  scraping  the  cracks  in  the  floor  and 
working  over  everything  about  the  mill  or  under  it  as 
well  as  the  tail-sluice  below  the  property.  Save  all  the 
chips,  screen  frames  and  any  wood  that  has  been  in 
use  in  the  battery  and  sluices,  burn  them  to  ashes  011  an 
iron  plate  and  amalgamate  the  ashes.  After  the  cast- 
ings have  become  dry,  examine  them  thoroughly,  and 
remove  every  speck  of  amalgam,  even  if  some  of  the 
iron  is  broken  off  with  it.  Hammer  the  old  screens  and 
scrape  off  all  the  rust;  while  all  small  bits  of  iron,  even 
that  saved  by  the  magnet,  should  be  mixed  with  salt 
and  dampened  occasionally,  and  spread  out  in  the  sun 
where  it  is  exposed  to  the  weather.  Every  six  months 
this  is  run  through  the  clean-up  barrel  or  clean-up  pan, 
whichever  is  employed. 

The  floor,  on  which  are  placed  the  plates,  is  given  a 
slope  towards  the  concentrators,  and  at  the  end  of  this 
floor  a  gutter  is  placed  which  will  catch  all  the  sweep- 
ings and  water  that  may  flow  down.  This  gutter  must 


HINTS  ON  AMALGAMATION.  55 

have  a  slight  grade,  ending  in  a  wooden  box  or  a  pipe, 
to  carry  off  the  waste,  but  in  each  gutter  one  or  two 
riffles  a  couple  of  inches  high,  are  placed  before  the 
overflow  pipe  is  reached.  Each  morning  the  plate-floor 
is  swept  thoroughly  to  this  gutter,  or  in  summer  washed 
down  with  the  hose,  and  a  stream  of  water  of  moderate 
strength  is  occasionally  run  through  the  gutter,  and  the 
concentrated  material  at  the  riffles  removed.  Every 
leak  from  the  plates  is  at  once  calked  and  stopped,  as 
where  the  sand  goes  some  of  the  quicksilver  and  amal- 
gam will  go,  even  if  a  panning  test  might  not  show  an 
appreciable  quantity.  We  can  safely  handle  all  the 
dirt  on  this  floor,  as  we  have  taken  especial  pains  to 
prevent  any  drippings  of  grease,  coal  oil,  or  other  dele- 
terious substances  from  coming  in  contact  with  the 
plates  or  their  environs. 

One  other  question  has  properly  to  be  considered,  and 
that  is  the  temperature  of  the  air,  and  the  battery  water, 
in  regard  to  its  action  on  the  amalgam.  We  see  the 
effect  of  heat  in  the  expansion  and  contracton  of  mer- 
cury in  thermometers  without  changing  the  weight  in 
the  least.  We  also  find  that  our  bowl  of  cleansing 
quicksilver  will  have  a  very  appreciable  amount  of 
crystalline  amalgam  after  the  first  cold  night.  There- 
fore, we  have  these  deductions  to  make:  As  the  cold 
increases,  the  quicksilver  becomes  more  viscous  and 
slower  in  motion,  and  it  will  not  dissolve  amalgam,  and 
to  increase  the  cold  beyond  a  certain  point  the  mass 
is  so  lacking  in  its  lively  characteristic,  that  it  will  re- 
quire more  in  quantity  and  with  the  least  beneficial  re- 
sults. According  to  actual  experience  this  temperature 
prohibitive  to  good  work  is  that  of  25  degrees  Fahren- 
heit or  lower.  With  an  increase  of  temperature,  the 
quicksilver  expands,  becomes  more  fluent,  runs  easier 


56  HINTS  ON  AMALGAMATION. 

and  will  carry  much  more  fine  gold  in  solution,  and  we 
are  enabled  to  keep  more  perfect  control  over  our  op- 
erations. To  any  one  accustomed  to  amalgamating 
"wet,"  a  low  temperature  will  be  of  most  benefit  though 
in  no  case  will  perfect  work  be  done.  In  wet  amalga- 
mation the  cold  viscous  quicksilver  will  form  a  pasty 
mass,  easily  collected  with  a  rubber,  but  as  soon  as  the 
temperature  rises  to  summer  heat,  there  is  a  great  di- 
vergence between  the  coarse  amalgam  and  the  fluid 
quicksilver,  and,  as  a  result,  the  upper  part  of  the  plates 
becomes  incomprehensibly  hard  and  dry,  in  spite  of  an 
increase  in  the  quantity  added,  while  the  more  lively 
and  thinned  quicksilver  runs  rapidly  off  the  plates,  is 
floured  and  lost,  carrying  with  it  the  increased  quantity 
of  gold  it  is  now  capable  of  dissolving,  lost  forever. 
As  a  result,  there  is  a  poor  efficiency  of  work  that  the 
amalgamator  cannot  explain  even  to  himself. 

In  pan-amalgamation  of  silver  ores,  the  pulp  is  heated 
to  the  boiling  point  of  water,  either  by  live  steam,  or  a 
false  bottom,  and  all  have  acknowledged  this  to  be  es- 
sential even  on  pure  chloride  ores,  not  only  on  account 
of  the  chemical  action,  but  also  to  put  the  quicksilver 
in  its  most  efficient  condition.  In  the  cheaper  gold 
amalgamating  this  can  not  be  done,  economically,  owing 
to  the  steady  influx  of  cold  water  through  the  batteries, 
but  common  sense  will  show  the  benefit  of  having  the 
battery  water  as  warm  as  consistent  with  expense  and 
the  health  of  the  employes.  In  summer,  for  all  prac- 
tical purposes,  the  ditch  or  spring  water  becomes  suffi- 
ciently warm  in  passing  through  the  water-tank  and 
pipes,  not  to  interfere  with  the  efficiency  of  the  quick- 
silver. But  in  winter,  except  in  the  tropics,  the  water 
comes  from  melting  snow,  and  it  is  very  little  above  freez- 
ing, and  unless  remedied,  it  is  better  to  hang  up  tin 


HINTS  ON  AMALGAMATION. 


57 


mill  during  the  cold  weather.  In  some  places  it  is  very 
dangerous  to  do  this,  not  only  on  account  of  the  burst- 
ing of  pipes,  but  when  once  frozen  up  it  will  be  difficult 
to  start  again  before  warm  weather  arrives.  It  is  im- 
perative then,  to  keep  the  mill  moving  and  thorough 
preparations  should  be  completed  during  the  early  fall, 


TANK 


/O  STAMPS 


Modern  Machinery. 


FIG.  18. 


to  provide  against  a  cold  snap,  even  if  of  rare  occur- 
rence. If  the  mill  is  run  by  steam,  this  is  very  easily 
attended  to,  but  wherever  possible,  mill-power  is  now 
derived  either  directly  from  water  under  pressure,  or 
indirectly  from  water  at  a  distance,  driving  an  electric 
plant. 

If  steam  is  employed,  the  waste  steam  is  conducted 
through  the  water  tank,  never  into  it  on  account  of  the 


58  HINTS  ON  AMALGAMATION. 

grease.  This  is  generally  sufficient,  but  in  an  excep- 
tionally cold  locality,  rather  than  add  fresh  live  steam 
directly  to  the  tank,  we  advise  the  following  arrange- 
ment: Before  carrying  the  water  to  the  battery,  pass 
it  through  a  coil  of  pipe  placed  around  the  steam-drum 
of  the  boiler  where  it  will  be  amply  \varmed  by  the 
waste  heat  emanating  from  the  surface  of  the  drum. 
As  this  will  make  the  water  uncomfortably  warm  in 
summer,  have  two  sets  of  pipes,  one  to  go  direct  to  the 
batteries  from  the  tank,  and  the  other  for  winter  use, 
leading  to  the  coil.  The  water  leaves  the  tank  in  one 
pipe,  but  within  a  couple  of  feet  this  pipe  enters  a  "T." 
With  short  nipples  from  the  other  two  outlets  and 
globe  valves  on  each  nipple,  the  water  can  be  diverted 
either  way  desired.  These  separate  pipes  are  jointed 
together  again  just  before  the  battery  pipe  is  reached 
by  another  "T,"  the  water  being  under  control  by  two 
globe  valves  arranged  as  in  the  first  instance.  Figure 
18  will  partially  explain  the  plan. 

In  a  mill  where  the  power  is  either  water  or  elec- 
tricity, the  building  is  made  tight  by  battening  all  the 
cracks,  keeping  the  doors  shut,  and  having  all  the  panes 
of  glass  in  the  windows.  Have  a  large  wood  stove,  at 
least  three  feet  long,  and  have  plenty  of  wood,  not  only 
for  the  comfort  of  the  employes,  who  will  attend  to 
their  work  better,  but  also  for  the  benefit  of  the  amal- 
gamation. In  a  cold  country  it  is  necessary  to  have  a 
small  boiler  solely  to  generate  steam  to  heat  the  water 
in  the  tank. 

In  some  localities  where  water  is  scarce  or  requires 
pumping  to  elevate  it  above  the  mill,  the  water  that 
conies  from  the  mine  is  used  in  the  battery.  This 
does  not  require  heating  unless  the  reserve  tank  is  very 
large  and  the  weather  very  cold.  In  most  mines  the 


HINTS  ON  AMALGAMATION.  59 

drainage  "water  will  not  hurt  the  amalgamation,  but  the 
acid  in  solution  from  the  decomposition  of  the  sul- 
phides, and  the  mud  and  slimes,  are  a  source  of  vexa- 
tious delays  and  consequent  expense.  The  acid  eats  the 
screens  and  they  break  very  quickly,  and  the  slimes 
choke  the  pipes  and  soon  fill  the  receiving  tank,  unless 
it  is  very  large.  Therefore,  it  is  better,  if  possible,  to 
use  spring  and  surface  water  in  preference  to  that 
pumped  from  the  mine,  the  only  advantage  of  the  latter 
being  its  uniform  temperature  the  year  round. 


CHAPTER  III. 
CLEANING   UP. 

As  the  amalgam  accumulates  in  battery  and  on  the 
plates,  a  certain  time  in  each  month  must  be  taken 
to  remove  it  all,  not  only  to  get  the  money  locked  up, 
but  to  do  the  necessary  repairing  to  the  mill  for  a 
coming  run.  It  is  far  better  to  appoint  a  regular 
day  and  adhere  to  it  as  near  as  possible,  as  the  cleaning 
up  when  the  owner  happens  to  be  at  the  mine,  or  the 
superintendent  feels  like  it,  always  comes  when  new 
shoes  and  dies  are  not  required,  and  often  when  the 
ore  is  just  in  the  best  condition  for  profitable  work 
in  that  month.  According  to  the  size  of  the 
mill  and  the  richness  of  the  ore,  this  day  should  be 
set  aside  either  once  or  twice  a  month.  Of  course,  in 
certain  localities  it  is  not  advisable,  for  obvious  reasons, 
to  have  exactly  the  same  day  in  each  month,  and  it 
cannot  be  too  strongly  impressed  on  those  in  power, 
to  keep  the  exact  day  to  themselves  until  the  morning 
that  has  been  set,  when  instructions  are  given  to  the 
millmen  to  hang  up,  and  the  night  shift  to  work  over- 
time, in  the  effort  to  finish  the  actual  cleaning  and  re- 
pairing and  start  the  mill  as  soon  as  possible.  If  the 
mining  property  is  isolated,  with  little  communication 
with  the  outside  world,  a  regular  day,  once  or  twice  a 
month,  does  no  harm;  but  in  a  community  where  there 
are  numerous  persons  unconnected  in  any  way  with  this 
particular  property,  and  a  section  subject  to  a  constant 
influx  and  outflow  of  persons,  whether  tramps  or  people 


HINTS  ON  AMALGAMATION.  61 

on  special  business,  it  is  on  the  safe  side  to  keep  the  date 
secret  when  the  long  accumulations  are  reduced  to  a 
portable  shape. 

For  this  reason  we  have  advised  the  preliminary 
preparations  of  a  goodly  stock  of  scrapers,  sharply-cut 
rubbers,  and  the  making  of  the  wooden  wedges  for  the 
shoes,  to  be  always  on  hand  and  ready  at  a  moment's 
notice,  so  that  no  estimate  of  the  special  day  can  be 
made  from  observing  the  preliminary  preparations. 

In  all  mines  we  find  rich  ore,  medium  grade,  and  poor 
ore,  and  an  efficient  superintendent  will  try  to  work 
all  these  together  in  the  proper  proportions  to  insure 
dividends,  and  yet  leave  no  ore  carrying  value  in  the 
mine.  A  "tenderfoot"  owner  will  be  highly  pleased  with 
large  profits  as  long  as  they  last,  but  is  always  unwilling 
to  part  with  some  of  this  profit  for  future  development, 
when  the  mine  has  been  robbed  of  its  richest  ore. 
Therefore,  it  is  advisable,  in  the  beginning  of  a  run, 
to  work  up  for  some  time  the  poorer  ore  of  the  mine, 
bringing  the  product  up  to  a  regular  amount  by  extract- 
ing more  or  less  of  the  richest  ore  as  required.  Now 
it  depends  not  only  on  the  size  of  the  mill,  but  also  on 
the  value  of  the  ore,  whether  the  mill  is  stopped  for 
clean-up  once  or  twice  a  month.  Should  all  the  ore  be 
low  grade,  we  cannot  afford  to  lose  any  more  time  than 
we  can  possibly  help,  and  should  only  take  one  day  in 
each  month,  as  our  dies  and  shoes  can  be  arranged  to 
last  that  time  without  renewal.  Even  if  we  remove 
them  before  their  usefulness  has  ended  we  make  more 
money  owing  to  the  increased  production.  In  a  custom 
mill,  after  each  lot  of  ore  is  worked,  of  course  a  thorough 
and  general  clean-up  must  be  made,  as  gold  ores  are 
not  safe  to  buy  outright,  with  the  limited  means  of  ac- 
curate sampling  which  is  generally  at  our  service  in 
countries  remote  from  smelters. 


62  HINTS  ON  AMALGAMATION. 

In  a  mill  running  steadily  on  ore  from  one  mine,  we 
can  afford  to  allow  a  little  of  the  value  to  remain  un- 
taken  at  each  clean-up,  as  it  will  have  an  average  result 
in  six  months  or  a  year,  and  in  reality  give  more  money 
from  a  greater  production.  Most  superintendents,  on 
clean-up  day,  remove  all  the  dies  from  all  the  batteries, 
to  get  the  amalgam  in  the  sand  and  ore  which  is  packed 
around  them,  from  two  weeks'  work,  and  then  replace 
these  partly  worn  dies  for  another  run.  We  consider 
this  to  be  a  great  loss  in  a  year's  run,  and  a  case  of 
greatly  mistaken  economy  for  several  reasons. 

When  we  first  put  in  the  new  dies,  they  were  very 
heavy,  and  so  kept  their  position,  and  the  tops  were 
absolutely  true.  Before  there  was  a  chance  of  changing 
position  they  became  cemented  with  the  rock  and  sand 
so  as  to  become  an  integral  part  of  the  mortar.  Though 
the  stamps  turn  at  each  revolution  of  the  cam  shaft, 
both  the  shoe  and  die  wear  unevenly,  but  each  shoe 
after  a  few  days  will  form  the  greatest  crushing  surface 
with  its  own  particular  die,  in  its  original  position,  which 
has  become  as  fixed  as  if  it  were  welded  to  the  mortar. 
This  situation  will  continue  till  either  the  shoe  or  die 
break  from  the  thinness  attained  through  the  steady 
wearing  away  of  the  iron.  In  addition  to  this,  the 
quantity  of  amalgam  which  settles  through  this  cement 
will  not  be  of  sufficient  amount  in  any  one  battery,  to 
diminish  the  total  output  to  such  an  extent  as  to  be 
of  special  moment  to  secure  at  that  particular  time, 
while  in  a  year's  work  it  will  return  a  much  better  aver- 
age. Now  suppose  partially  worn  dies  are  removed,  the 
gravel  extracted  and  the  mortar  prepared  for  their  re- 
placing. The  tops  of  the  dies  are  now  uneven,  perhaps 
worn  more  on  one  side  than  the  other,  or  cupped,  but 
the  shoe  corresponding  to  each  die  is  worn  the  same, 


HINTS  ON  AMALGAMATION.  63 

and  to  replace  the  dies  exactly  in  the  same  relative  po- 
sition is  well  nigh'  impossible,  even  with  the  greatest 
care,  and  a  useless  waste  of  time  as  well.  The  result 
is,  that  a  point  or  edge  of  a  shoe  strikes  on  a  point  or 
edge  of  a  die,  offering  a  minimum  of  crushing  surface 
for  several  days,  and  using  up  unnecessarily  a  great 
deal  of  iron,  with  no  benefit  per  ton  of  ore  worked. 
The  lessened  weight  of  the  die  also  allows  it  to  jump 
from  the  blow  of  the  stamp,  before  the  gravel  has  be- 
come cemented,  and  we  are  specially  liable  to  a  cracked 
die,  or,  at  any  rate,  one  tilted  at  an  angle  to  its  base. 
After  a  couple  of  months  at  the  longest,  we  find  some  of 
the  batteries  with  worn  out  dies,  while  others  will  con- 
tinue till  our  next  clean-up  day.  We  replace  those 
worn  out,  and  leave  the  others,  after  digging  out  most 
of  the  cemented  gravel  around  them,  and  we  get  ready 
for  a  fresh  start  in  the  shortest  possible  time,  and  are 
again  making  money.  We  certainly  earn  no  additional 
money  on  clean-up  day;  we  only  collect  that  which  we 
have  previously  earned. 

The  previous  day  to  that  one  agreed  on,  we  examine 
all  the  shoes  and  mark  those  batteries  where  we  have 
to  re-shoe  and  put  in  new  dies,  while  other  shoes  which 
are  too  far  worn  to  last  a  whole  run  are  also  marked 
for  removal,  and  partially  worn  ones  which  have  ac- 
cumulated are  prepared  for  these  stamps.  A  close  ex- 
amination is  also  made  of  every  part  of  the  mill,  includ- 
ing the  engine,  if  run  by  steam,  and  whether  the  boilers 
require  cleaning.  In  the  case  of  steam  power,  the  order 
to  clean  up  is  given  the  night  before,  as  the  mill  must 
be  stopped  at  4  a.  m.  to  allow  the  boilers  to  cool  suffi- 
ciently to  be  blown  off.  A  regular  system  must  be 
drilled  into  the  minds  of  the  employees,  so  that  each  one 
knows  exactly  what  he  is  expected  to  do.  The  firemen 


64  HINTS  ON  AMALGAMATION. 

attend  to  the  boilers;  the  engineer  cleans  and  repairs 
the  engine,  taking  up  all  lost  motion,  and  then  looks 
over  all  the  line  shafts  and  pulleys,  tightening  up  the 
bolts  on  wooden  pulleys,  relaces  or  rivets  those  belts 
that  require  it,  and  does  all  the  other  mechanical  re- 
pairing, assisted  by  the  night  engineer.  The  concen- 
trator men  thoroughly  clean  the  machines;  go  over  the 
plane  of  the  table  with  straight  edge  and  level,  replace 
all  worn  out  castings,  lace  the  driving  belts,  and  get 
everything  in  apple-pie  order.  The  man  who  attends  to 
the  rock-breaker  cleans  it  of  all  grease  and  replaces 
worn  out  shoes  and  dies,  assisted  in  this  or  any  babbit- 
ing by  the  engineer.  The  battery  men  and  all  others 
connected  with  the  mill,  who  have  no  special  duty,  are 
under  the  direct  supervision  of  the  foreman,  and  help 
him,  first  in  removing  the  amalgam  plates  to  the  clean- 
up room,  and  then  to  extract  the  sand  from  the  batteries, 
clean  off  all  the  amalgam  from  the  aprons  and  get  the 
batteries  in  general,  ready  for  as  speedy  a  return  to 
starting  as  possible,  and  it  is  with  their  work  that  spe- 
cial instructions  must  be  given. 

Orders  are  given  to  stop  the  mill  at  a  certain  time, 
and  a  few  minutes  before,  the  feeders  are  shut  off,  and 
boards  put  over  the  throats  of  the  mortars  to  prevent 
any  more  rock  being  jarred  into  the  batteries.  When 
the  stamps  begin  to  strike  iron,  two  methods  can  be 
pursued,  either  hang  up  all  the  stamps  or  reduce  the 
speed  of  the  mill  down  to  about  thirty-five  drops  per 
minute,  and  allow  the  stamps  to  drop  till  the  water 
comes  through  the  screens  clear,  though  still  carrying 
some  sand.  We  prefer  this  last  method  for  several 
reasons:  we  have  less  gravel  to  handle,  the  chuck-blocks 
and  all  parts  of  the  mortar  are  clean,  and  therefore 
visible,  and  any  quicksilver  or  amalgam  which  is  in  the 


HINTS  ON  AMALGAMATION.  65 

rock  on  top  of  the  dies  has  been  thrown  out  or  settled 
below  the  tops.  The  method  advocated  by  some,  to 
hang  up  all  but  one  battery,  and  feed  this  surface  rock 
through  it,  not  only  takes  a  longer  time,  but  requires 
the  workmen  to  expose  themselves  to  a  possible  but  not 
probable  accident,  by  working  under  the  stamps  with 
the  cam  shaft  in  motion,  and  they  do  the  work  in  con- 
sequence carelessly,  and  take  a  much  longer  time. 

As  soon  as  the  stamps  are  hung  up  the  water  is  turned 
off,  and  preparations  at  once  started  to  clean  up  the 
mill. 

First,  the  splash  plates  are  washed  and  laid  across  the 
lower  apron  plate.  Second,  the  screens  are  removed, 
washed  over  the  plate  and  carried  to  the  clean-up  room. 
Third,  the  lower  keys  are  driven  out  and  the  chuck- 
blocks  carefully  removed  and  washed  over  the  plates 
and  carried  to  the  clean-up  room.  Fourth,  the  lip  plate 
is  washed  on  both  sides  and  placed  on  the  lower  apron. 

The  mill  crew  is  now  divided.  One  man  is  put  in  the 
clean-up  room  and  chisels  off  the  amalgam  from  the 
chuck-blocks  directly  into  the  tray.  A  second  moves 
the  upper  halves  of  the  apron  plates  down  over  the 
lower  halves,  after  thoroughly  washing  down  all  the 
gravel  and  dirt  to  the  trap.  He  then  scrapes  the  amal- 
gam from  lip  plate  and  splash  plate  on  the  upper  apron. 
These  two  are  the  day  and  night  shift  amalgamators. 
The  others  of  the  crew  remove  the  top  gravel  from  the 
mortars  and  dump  it  into  the  feeder  of  one  battery. 
When  this  top  gravel  is  taken  out  to  the  top  of  the 
dies  the  balance  of  the  gravel  is  picked  out  around  the 
dies,  and  those  dies  extracted  which  require  removal. 
This  cemented  gravel  is  dumped  into  the  barrel  or  placed 
in  a  box  alongside  of  the  clean-up  pan,  and  the  mortar 
is  thoroughly  cleaned,  all  adhering  amalgam  on  shoes, 


66  HINTS  ON  AMALGAMATION. 

sides  and  lip  of  mortar  being  chiseled  off.  The  worn  out 
shoes  are  driven  off  the  stems,  and  the  worn  out  wedges 
put  into  a  box  for  examination  and  future  burning. 
The  new  dies  are  placed  in  position,  and  the  new  shoes 
with  the  circle  of  wedges  placed  on  top  of  the  dies. 
The  partitions  are  taken  out  of  the  traps,  the  water  re- 
moved with  a  sponge  and  the  settlings  added  to  the  pulp 
taken  from  the  battery.  The  old  shoes  and  dies  are 
washed  in  a  tub,  the  amalgam  roughly  chipped  off  and 
the  sediment  added  to  that  in  the  barrel. 

These  men  now  tighten  all  the  bolts  around  the  bat- 
tery and  clean  the  stems  and  cams  of  every  particle  of 
grease,  using  a  table  knife,  coal  oil  and  old  sacks. 
When  this  is  done,  wooden  blocks  are  put  on  the  dies, 
the  exact  height  the  drop  of  the  stamps  is  required  to  be. 
The  feed  stamp  is  given  a  half-inch  more  drop,  and  the 
two  end  stamps  a  quarter  inch  more  than  the  others, 
viz.,  No.  2  and  No.  4,  and  these  stamps  are  set  by  their 
tappets. 

The  amalgamators  and  foreman  have,  in  the  same 
time,  scraped  off  all  the  amalgam  from  the  chuck- 
blocks  and  all  the  plates,  and  it  is  stored  in  kettles  and 
pans,  ready  for  the  clean-up  barrel;  in  fact,  should  be 
dumped  into  the  barrel  as  fast  as  collected  to  get  it  out 
of  harm's  way.  The  upper  apron  is  put  in  place,  and  the 
lip  plate,  splash  plate  and  chuck-block  for  each  battery 
put  on  the  lower  apron.  The  engine  or  water-wheel  is 
now  started  slowly  and  the  shoes  driven  on,  and  these 
shoes  are  now  set  by  the  blocks  as  the  others  have 
been. 

All  the  amalgam  and  gravel  is  in  the  clean-up  barrel. 
Some  water  and  at  least  40  pounds  of  quicksilver  are 
added,  though  the  amount  of  quicksilver  depends  on  the 
quantity  of  amalgam  to  be  cleaned,  and  sometimes  100 


HINTS  ON  AMALGAMATION.  67 

pounds  and  even  more  are  required.  We  will  explain 
the  use  of  the  barrel  first,  and  afterwards  the  method 
of  procedure  where  a  pan  is  employed. 

The  barrel  is  placed  opposite  the  door  to  the  clean-up 
room,  in  a  line  with  the  batteries,  and  is  driven  by  a  belt 
connecting  with  the  rock-breaker  line-shaft.  Directly 
under  it  is  placed  a  water-tight  box  12  inches  high, 
and  in  the  center  of  this  box  a  worn  out  die,  on  which 
to  set  one  of  the  enameled  pails.  On  the  rear  side  of  this 
box  is  an  overflow  sluice,  on  which  is  placed  a  silvered 
plate  three  or  four  feet  long.  There  are  two  openings 
in  the  barrel,  one  being  a  manhole,  to  dump  the  material 
to  be  worked,  and  the  other  a  screw  plug  one  inch  in 
diameter,  through  which  the  material  is  drawn  on 
completion  of  the  grinding.  To  accomplish  this  attrition 
there  are  put  into  the  barrel  several  pieces  of  old  shaft- 
ing from  one  to  two  feet  long,  round  cannon  balls  and 
pieces  of  broken  shoes  and  dies  of  all  sizes,  at  least  a 
total  weight  of  800  pounds.  The  cannon  balls  alone  do 
not  do  either  rapid  or  thorough  work,  but  with  the  ir- 
regularly shaped  and  sized  broken  castings,  all  the 
ore  is  quite  rapidly  ground  to  a  slime. 

The  cap  of  the  manhole  is  screwed  on  tightly,  the  joint 
being  made  quicksilver-proof  with  a  rubber  gasket.  The 
driving  belt  is  connected  with  the  pulley  on  the  line 
shaft,  and  the  engine  or  water-wheel  started.  The  bar- 
rel should  not  run  very  fast,  as  the  centrifugal  force 
exerted  on  the  iron  and  material  will  hinder  the  grind- 
ing which  is  done  by  the  rolling  of  the  castings  over  the 
pulp.  These  heavy  castings  are  carried  up  the  side,  till 
their  weight  overcomes  their  inertia,  when  they  slide 
and  roll  back  to  the  bottom,  and  a  high  speed  will  tend 
to  carry  them,  if  not  all  the  way  around,  at  least  so  far 
that  they  will  only  drop  and  not  slide  over  the  pulp. 


68  HINTS  ON  AMALGAMATION. 

We  consider  that  Mr.  Preston  makes  a  great  mistake  in 
his  treatise,  where  he  advises  a  speed  of  70  revolutions 
per  minute,  as  this  speed  should  never  be  over  15  revo- 
lutions, and  our  practice  has  been  to  use  from  7  to  10, 
when  the  pulp  is  thoroughly  ground  inside  of  twelve 
hours. 

As  soon  as  the  barrel  is  started,  the  night  shift  go  off 
duty,  and  if  it  is  late  in  the  day,  the  day  shift  remain 
on  duty  till  midnight.  The  day  shift  now  dress  all  the 
plates  with  the  dressing  mixture,  thoroughly  amalga- 
mate the  chuck-block,  lip,  and  splash  plates  with  quick- 
silver, throw  some  rock  into  the  battery,  replace  every- 
thing, including  new  screens,  and  start  on  a  fresh  run. 
All  the  implements  used  are  cleaned  and  taken  to  the 
clean-up  room,  the  floor  is  cleaned  and  all  the  mill  put 
in  apple-pie  order  once  more. 

In  scraping  the  chuck-blocks,  we  take  everything  down 
to  the  clean  copper,  but  great  care  must  be  exercised  in 
scraping  the  silvered  plates,  not  to  go  into  the  silver 
coating  at  all.  This  is  not  so  very  difficult,  but  for  this 
reason  the  work  should  be  done  by  the  amalgamators, 
or  those  who  are  careful  in  their  operations.  There 
is  a  great  difference  in  the  "feel"  of  the  scraper  when 
going  through  amalgam  or  into  the  silver  the  latter 
being  very  much  harder  and  smoother.  In  fact  it  very 
frequently  feels  like  the  surface  of  glass.  The  scrapers 
must  have  perfectly  true  edges  and  be  very  sharp,  with 
an  end  like  a  wood  chisel.  The  flat  side  is  put  against 
the  plate  and  a  steady  pressure  exerted,  never  a  chip- 
ping or  striking  motion.  The  barrel  is  allowed  to  run 
till  there  is  a  steady  swish  and  no  grinding  is  heard. 
To  be  on  the  safe  side,  it  is  better  not  to  open  it  till 
the  next  morning  when  it  is  certainly  ground  most 
thoroughly.  The  belt  is  thrown  off  and  the  barrel  turned 


HINTS  ON  AMALGAMATION. 


69 


till  the  manhole  is  on  top.  The  cap  is  removed  and 
washed  over  the  manhole,  and  the  enameled  pail  (placed 
on  top  of  the  die  directly  under  the  screw-plug),  and  the 
box,  are  filled  with  water  from  a  hose,  which  hose  is 
fastened  to  and  kept  in  the  pail.  The  screw-plug  is 
removed,  and  as  the  amalgam,  quicksilver  and  slimes 
flow  out  into  the  pail,  it  is  constantly  stirred  with  a  wooden 
or  iron  paddle,  so  as  to  keep  the  contents  in  constant 


ModernMachinery. 


agitation.  Whenever  no  more  will  run  out  by  itself, 
the  hose  is  turned  into  the  barrel,  and  the  pieces  of  iron 
taken  out,  each  piece  being  thoroughly  washed.  All  this 
time  the  contents  of  the  pail  are  kept  agitated,  so  that 
only  the  heavy  amalgam  and  iron  remain,  all  the  sand 
flowing  into  the  big  box  and  from  there  over  the  waste 
sluice  plate.  After  all  the  iron  is  removed,  the  inside 
of  the  barrel  is  thoroughly  cleaned  with  a  broom  and 
the  clear  water,  and  our  clean-up  is  finally  collected  in 


70  HINTS  ON  AMALGAMATION. 

the  pail,  but  it  still  requires  some  work  which  must  now 
be  done  by  hand.  We  give  a  cross  section  of  barrel,  pail 
and  box  in  Fig.  19. 

The  pail  is  carried  to  the  clean-up  room  and  the  super- 
imposed sand  and  iron  panned  in  small  quantities  at  a 
time.  The  sand  is  washed  away  and  the  iron  picked 
out  by  hand  and  extracted  with  the  magnet,  until 
nothing  but  the  quicksilver  and  amalgam  is  left.  This 
is  squeezed  into  balls  of  convenient  size,  and,  with  that 
collected  each  day,  is  now  ready  for  retorting.  In  some  ex- 
ceptionally unsafe  localities  it  might  not  be  advisable 
to  delay  the  retorting  till  the  day  after  the  clean-up,  and 
in  that  case  all  the  dirty  amalgam  is  kept  separate  from 
the  gravel  and  sand,  and  is  first  cleaned  by  itself  in  the 
barrel.  In  this  case  there  is  only  need  of  putting  in  the 
cannon  balls.  The  machine  will  clean  and  soften  the 
amalgam  in  less  than  an  hour,  when  it  can  be  drawn 
off  as  described  above,  the  iron  extracted  and  retorted 
at  once.  After  this  is  done,  all  the  sand  and  gravel  is 
put  into  the  barrel,  together  with  the  different  sized 
pieces  of  iron,  and  is  ground  till  the  next  day.  The 
amalgam  resulting  from  this  is  stored  in  the  strong  box 
till  the  next  clean-up. 

Though  the  barrel  is  more  generally  used  in  gold  mills, 
some  mill  men  prefer  a  grinding  pan,  which  is  at  all 
times  open  to  inspection,  and  can  be  fed  with  fresh  ma- 
terial without  stopping  and  cleaning  out  the  previous 
charge.  Differing  from  a  silver-amalgamating  pan,  this 
one  combines  the  work  of  both  the  grinding  and  amalga- 
mating pan  and  the  settler.  The  pan  should  have  iron 
shoes  and  dies,  and  three  outlets  at  different  heights, 
closed  by  wooden  plugs,  in  addition  to  the  main  duct 
set  below  the  bottom  of  the  die.  The  overflow  outlets 
conduct  the  tailings  directly  over  a  sluiceplate,  while 


HINTS  ON  AMALGAMATION.  71 

the  main  duct  discharges  into  a  water-tight  box,  fixed 
with  old  die  and  pail.  The  overflow  from  this  is  carried 
to  the  same  silvered  plate  that  the  slimes  ran  over.  This 
is  shown  in  a  cross-section,  Fig.  20,  which  represents 
only  the  outlet  part  of  the  pan.  The  speed  should  be 
about  30  revolutions  per  minute,  and  the  modus  oper- 
and! is  as  follows:  The  amalgam  alone  is  first  ground 
with  the  muller  down  and  a  sufficient  addition  of  quick- 
silver to  thin  it  and  only  a  little  water.  When  thor- 
oughly ground,  which  should  be  done  in  an  hour  at  the 
longest,  water  is  added,  the  muller  slightly  raised,  and 
the  overflow  plugs  opened  in  succession,  with  clear 
water  constantly  running  in  till  there  are  no  more 
slimes  running  out.  Then  the  main  duct  is  opened  and 
the  amalgam  and  quicksilver  run  into  the  pail.  After 
all  has  run  out  that  will,  the  machine  is  stopped  and  the 
balance  swept  out  with  the  whisk  broom.  After  the 
amalgam  is  cleaned,  a  charge  of  the  gravel  is  put  in 
and  40  pounds  of  quicksilver,  and  ground  moderately, 
when  all  that  will  run  down  to  the  lowest  overflow  plug, 
after  thinning  with  water,  is  allowed  to  escape.  The 
plugs  are  then  put  in  and  it  is  filled  up  with  more  of 
the  gravel.  This  is  continued  till  all  of  the  scrapings 
are  in  the  pan.  When  this  is  all  ground,  the  main  duct 
is  opened  at  the  very  last,  and  the  amalgam,  quick- 
silver and  iron  are  run  into  the  pail,  and  when  the  iron 
is  separated  the  amalgam  is  panned  and  squeezed. 

The  advantages  of  the  barrel  over  the  pan  are:  First, 
it  takes  less  power  to  run.  Second,  it  does  not  require 
so  much  skill  to  handle.  Third,  it  is  a  thorough  grinder 
and  amalgamator.  Fourth,  the  cost  of  wear  and  tear 
is  practically  nothing,  as  worn  out  castings  are  used. 
Fifth,  its  contents  cannot  be  tampered  with,  unless  the 
machine  is  stopped. 


72  HINTS  ON  AMALGAMATION. 

The  disadvantages  are:  First,  it  can  only  be  run  by 
hearing.  Second,  only  one  charge  at  a  time  can  be  run, 
and  not  continuously  as  in  a  pan.  Third,  the  separation 
of  sand  from  amalgam  has  to  be  done  on  discharging  the 
contents,  when  the  pulp  is  thick  and  capable  of  carry- 
ing off  values. 

As  the  advantages  considerably  more  than  balance 
the  objections  to  it,  we  would  advise  the  employment  of 
a  barrel. 


CHAPTER  IV. 
RETORTING  AND  MELTING. 

The  kind  of  a  retort  we  require  in  our  mill-plant, 
depends  entirely  on  the  amount  of  amalgam  we 
have  to  distill  at  each  clean-up.  There  are  two 
varieties  in  use,  the  stationary  ones,  always  used  in 
silver  mills,  but  only  employed  in  gold  mills  when  the 
amount  of  amalgam  runs  over  1,500  ounces;  and  port- 
able retorts  in  sizes  holding  from  30  ounces  and  up- 
wards. If  the  number  of  stamps  exceeds  40,  and  the 
ore  is  of  good  grade,  we  will  require  a  stationary  re- 
tort, but  its  use  is  of  much  less  importance  in  general 
mill  work  than  tbe  portable  ones. 

Where  retorting  of  large  quantities  is  required,  we 
must  have  a  building  entirely  separate  from  the  mill. 
This  building  will  contain  one  room  for  the  retorting 
and  melting  furnaces,  and  one  for  the  assaying  and 
chemical  department,  with  a  small  room  in  which  the 
delicate  balances,  assay  accounts  and  such  things  which 
require  care,  are  kept.  The  retort  is  p*;A  in  the  center 
of  the  room  and  the  outlet  from  the  fire  box  extends 
to  a  chimney  placed  to  one  side.  Into  this  chimney, 
from  the  other  side  come  the  flues  from  the  two  melting 
furnaces  and  the  muffle  furnace.  All  around  the  fur- 
naces the  floor  is  covered  with  iron  plates  at  least  four 
feet  wide,  the  remainder  of  the  flooring  being  brick 
set  very  closely  together.  The  retort  is  placed  hori- 
zontally and  is  closed  by  a  cap  covering  the  whole  in- 
terior diameter,  while  the  outlet  for  the  escape  of  the 

73 


74  HINTS  ON  AMALGAMATION. 

quicksilver,  is  a  small  orifice  at  the  top  of  the  rear 
end,  from  which  it  is  conducted  by  a  water-jacketed 
pipe  to  a  receiver,  which  is  an  iron  tank  filled  with 
water.  The  balls  of  amalgam  are  placed  loosely  in  trays 
which  just  fit  the  contour  of  the  bottom  of  the  retort. 
These  trays  are  first  thoroughly  coated  with  chalk  to 
prevent  the  gold  sticking  to  the  iron  when  softened  by 
the  heat.  When  all  the  trays  are  pushed  in,  the  cap 
is  put  on  and  keyed  very  tightly.  Now  a  tight  joint 
cannot  be  made  with  iron  against  iron,  and  no  gaskets 
will  stand  the  heat,  so  we  must  find  a  joint  unaffected 
by  the  heat  or  the  action  of  the  quicksilver.  There  are 
several  substances  at  our  disposal,  and  the  choice  de- 
pends only  on  the  presence  of  one  or  the  other  and  its 
relative  cost.  The  luting  material  can  be  pure  clay, 
either  white  fire  clay  or  colored,  as  the  heat  is  not  suf- 
ficiently high  to  melt  or  even  thoroughly  bake  it.  The 
most  common  material  employed  is  sifted  woodashes, 
either  mixed  with  water  alone  or  with  the  addition 
of  salt.  Either  material  is  first  screened  through  the 
40  mesh  sieve,  and  all  lumps  in  the  clay  or  cinders  in 
the  ashes  thrown  away.  A  small  portion  is  mixed  and 
puddled  with  a  little  water,  until  it  can  be  moulded  in 
any  form  without  breaking,  and  yet  carries  no  surplus 
water.  As  the  puddling  is  carried  on,  either  water 
or  ashes  are  added  till  the  right  quantity  of  the  proper 
consistency  is  obtained.  At  first  a  novice  is  apt  to  add 
too  much  water,  the  paste  seeming  to  be  too  dry,  but 
on  working  it  with  a  knife,  it  grows  softer  and  more 
liquid,  so  that  only  after  considerable  puddling  and 
slight  additions  of  ashes  is  it  possible  to  get  it  thick 
and  at  the  same  time  soft.  When  ready  the  cover  is 
laid  in  a  horizontal  position  and  the  lute  put  all  around 
the  edge  in  the  recess  made  for  it.  It  is  put  on  quite 


HINTS  ON  AMALGAMATION.  75 

thick,  carefully  smoothed  with  the  knife  till  the  sur- 
face is  perfectly  homogeneous,  when  the  cover  is  placed 
exactly  in  its  place  against  the  retort  and  tightly  keyed. 
The  surplus  lute  is  squeezed  out  all  around  the  cover. 
This  is  scraped  off,  and  the  junction  between  cover 
and  retort  smoothed  with  the  knife. 

A  small  fire  of  shavings  and  wood  or  bark,  is  now 
started  and  the  retort  gradually  warmed,  care  being 
used  to  keep  a  small  fire  till  all  the  metal  is  thoroughly 
heated.  This  is  to  prevent  the  deflagration  of  the  amal- 
gam, as  well  as  any  danger  of  cracking  the  retort  itself. 
The  heat  is  gradually  raised  till  the  bottom  of  the  re- 
tort is  a  dull  red.  Then  the  quicksilver  will  begin 
to  vaporize.  No  fuel  but  wood  must  be  used,  and  there 
is  no  advantage  in  trying  to  hurry  the  distillation.  It 
will  take  just  so  long,  as  there  is  only  a  fixed  area 
for  its  escape  in  the  outlet  pipe,  and  if  this  is  crowded 
by  the  pressure  of  the  quicksilver  gas  in  the  retort, 
there  is  danger  of  some  escaping  before  the  condensa- 
tion takes  place,  thus  endangering  the  health  of  the 
operator  and  also  of  breaking  the  joint  where  the  con- 
densing pipe  is  fastened -to  the  retort  itself.  After  the 
quicksilver  begins  to  collect  in  the  tank,  the  heat  is 
slightly  raised  and  the  retort  kept  at  a  cherry  red  till 
the  amount  of  quicksilver  coming  from  the  pipe  slack- 
ens up.  The  pipe  is  now  gently  tapped  with  a  hammer 
occasionally  and  the  fire  kept  up  till  no  more  quick- 
silver, not  even  a  drop,  can  be  collected  on  holding 
the  hand  under  the  pipe  and  tapping  it  smartly.  When 
this  is  found  to  be  the  case,  the  fire  is  allowed  to  burn 
out,  or  is  drawn  and  the  retort  left  to  cool.  This  takes 
several  hours  on  account  of  the  mass  of  metal  which  has 
been  heated  so  thoroughly. 

For  this  reason,  we  try  to  start  the  fire  in  the  after- 


76  HINTS  ON  AMALGAMATION. 

noon,  and  finish  the  retorting  during  the  night.  As 
soon  as  it  has  become  thoroughly  heated,  it  is  safe  to 
leave  in  the  care  of  the  watchman  as  no  one  is  able  to 
open  the  retort  or  abstract  the  metal  as  long  as  it  re- 
mains so  hot.  It  is  rarely  cool  enough  to  open  with 
safety  till  7  a.  m.,  the  next  day,  and  it  should  not  be 
touched  till  the  arrival  of  the  one  in  authority.  When 
ready,  the  cap  is  removed  and  the  trays  taken  out  and 
placed  on  the  iron  plates  to  cool  still  more.  If  the  re- 
torting has  not  been  done  too  rapidly  and  with  too 
high  a  heat,  hard  to  get  with  wood  fuel,  the  gold  should 
still  be  in  its  pristine  balls,  now,  however,  porous  and 
spongy.  In  the  bottom  of  each  tray  we  always  find 
some  of  the  gold  joined  together,  being  partially  melted 
from  its  proximity  to  the  red-hot  iron;  but  it  can  be 
easily  broken  with  a  blow  of  the  hammer  into  conveni- 
ent weights  to  handle  for  the  subsequent  melting. 

At  most  mines,  the  amount  of  amalgam  at  each  cle^n- 
up  is  small  in  actual  bulk,  and  can  be  handled  with  the 
portable  retorts.  Each  mill. should  have  two  on  hand, 
of  different  sizes,  the  largest  according  to  the  rapacity 
of  the  mill  and  the  richness  of  the  ore,  capable  of  iiold- 
ing  in  one  charge  the  total  of  the  clean-up.  A  retort 
must  never  be  filled  more  than  three-quarters  of  its 
capacity.  The  danger  from  over-loading  is  not  appre- 
ciated by  the  average  person  till  a  serious  accident 
occurs.  Under  the  influence  of  the  heat  the  whole  mass 
swells  very  much,  and  we  have  seen,  from  putting  too 
much  amalgam  in,  first,  the  complete  choking  of  the 
outlet  pipe  by  amalgam,  and  then  when  the  pressure 
became  too  great  the  sudden  forcing  of  several  pounds 
of  amalgam  with  quicksilver  vapor,  into  the  receiving 
tank.  In  some  cases  if  the  retort  was  old  or  the  cap 
improperly  fastened,  a  very  serious  and  dangerous  acci- 


HINTS  ON  AMALGAMATION.  77 

dent  would  happen  from  the  explosion  of  the  retort 
itself. 

The  portable  retorts  are  in  two  shapes,  those  with 
a  flat  cover,  and  those  with  a  curved  cover  and  known 
as  the  Nevada  retort.  The  latter  style  is  very  much 
preferable,  as  it  gives,  under  all  circumstances,  A  re- 
serve space  for  the  quicksilver  vapor  and  allows  a 
little  more  latitude  in  filling  the  retort,  besides  giving 
a  much  stronger  keyway  and  general  fastening. 

Before  putting  in  the  amalgam,  every  part  of  the  re- 
tort must  be  examined.  First  see  that  the  pipe  is  tightly 
screwed  into  the  cover,  and  is  perfectly  clear,  tapping 
it  with  a  hammer  and  blowing  through  it.  With  a 
new  one,  be  sure  and,  coat  it  thoroughly,  because,  if 
the  gold  adheres  to  the  iron  in  any  one  place,  in  sub- 
sequent cooking  with  every  care  taken,  it  is  generally 
attached  to  the  same  place.  If  the  retort  has  been 
in  use,  remove  all  adhering  particles  of  gold  with  a 
chisel  and  coat  most  thoroughly.  We  have  a  choice 
of  two  coatings,  one,  which  we  consider  the  best,  is  of 
soft  chalk,  rubbed  on  dry  from  the  chunk  or  powdered, 
mixed  into  a  paste  with  water,  and  plastered  smoothly 
all  over  the  inside;  the  other,  a  thin  paste  of  sifted 
wood  ashes  and  water,  which  is  thoroughly  daubed  all 
over  the  interior.  If  a  paste  is  used,  the  retort  should 
be  dried  before  putting  in  the  amalgam.  The  quicksilver 
condensing  pipe  should  always  be  water- jacketed,  and 
can  be  bought  already  prepared  in  this  way.  This  jacket 
consists  of  an  iron  or  tin  pipe  two  to  four  inches  in 
diameter,  and  made  water  tight  at  each  end,  through 
which  the  condensing  pipe  passes.  At  the  lower  end, 
the  furthest  from  the  retort,  there  is  put  in  a  part  of 
a  hose  coupling  to  which  the  hose  conveying  the  cold 
water  can  be  screwed.  At  the  upper  end  Is  a  small 


78 


HINTS  ON  AMALGAMATION. 


outlet,  to  which  a  piece  of  quarter  inch  pipe  is  screwed. 
This  pipe  is  bent  and  carried  down  on  top  of  the  con- 
denser, discharging  into  the  kettle  which  receives  the 
metallic  quicksilver.  If  not  bought  with  the  retort, 
any  tinsmith  or  capable  engineer  can  make  a  tin  cyl- 
inder of  the  required  size,  solder  in  a  hose  coupling  at 
the  lower  end,  and  solder  the  whole  tightly  to  the  pipe 


at  each  end,     The  constant  flow  of  water  will  prevent 
any  melting  of  the  solder  (See  Fig.  21). 

Where  a  water-jacket  is  used,  the  end  of  the  outlet 
pipe  is  placed  a  little  below  the  surface  of  the  water 
in  the  receiving  kettle,  an  inch  being  ample.  Sometimes 
it  is  necessary  to  use  a  retort,  having  only  the  naked 
pipe  over  which  water  is  poured  from  a  dipper.  In  this 
case  care  must  be  taken  that  the  orifice  of  the  con- 
densing pipe  is  partly  out  of  the  water,  and  this  is  very 
rarely  looked  into  by  mill  men.  The  danger  of  a  diminu- 
tion in  the  heat  consists  in  the  creation  of  a  partial 
vacuum  in  the  retort,  which  then  sucks  up  water  from 
the  kettle  if  the  pipe  is  wholly  immersed.  This  water 
is  converted  into  steam  and  causes  an  explosion  of  great 


HINTS  ON  AMALGAMATION.  79 

danger.  With  part  of  the  orifice  out  of  the  water,  only 
air  is  sucked  up,  which  causes  no  sudden  increase  in  the 
internal  pressure;  but  we  are  confronted  with  another 
danger,  that  of  salivation  from  the  escaping  quicksilver 
gas,  unless  we  close  the  orifice  in  some  way.  Now  we 
wish  to  impress  this  point  very,  very  strongly  on  all 
those  intending  to  retort  the  amalgam  without  a  water- 
jacket.  Even  if  they  are  fortunate,  time  after  time, 
in  having  no  serious  accident,  they  will  always  be  more 
or  less  salivated,  and  it  takes  a  very  slight  exposure  to 
quicksilver  fumes  to  find  the  teeth  becoming  loose  and 
other  evidences  of  quicksilver  poisoning.  The  way  to 
prevent  it  is  this:  The  pipe  is  wrapped  with  burlaps  or 
gunny  sacks,  and  a  V  of  tin  placed  underneath,  sus- 
pended by  wire,  to  carry  the  water  poured  over  the 
upper  part  of  the  pipe,  away  from  the  fire.  This  sack- 
ing is  extended  several  inches  beyond  the  end  of  the 
pipe  and  into  the  water  of  the  receiving  kettle.  In  this 
case  the  pipe  must  be  straight  from  the  retort  to  the 
kettle,  with  no  bend,  as  shown  in  the  sketch  of  the 
water-jacketed  pipe.  The  wet  sacking  prevents  any 
escape  of  the  quicksilver  fumes,  and  yet  part  of  the 
orifice  of  the  pipe  is  out  of  water.  Should  a  partial 
vacuum  be  formed  inside  the  retort,  the  only  effect  is 
to  suck  the  gunny  sack  against  the  mouth  when  the 
air  enters  freely  through  the  web. 

The  retort  has  been  chalked,  all  parts  examined,  and 
the  amalgam  in  balls  ready  to  be  packed  in  it.  This 
packing  depends  on  the  subsequent  handling  of  the  re- 
tort-metal. Where  not  convenient  to  melt  into  a  bar  at 
the  mine,  it  is  just  as  well  to  ship  the  gold  just  as  it 
conies  from  the  retort,  but  in  that  case  we  want  to  have 
it  as  compact  a  mass  as  possible.  If  it  is  melted  at 
once  it  is  better  to  keep  it  in  its  original  balls  from 


80  HINTS  ON  AMALGAMATION. 

which  the  quicksilver  has  been  distilled.  When  the  re- 
tort metal  is  shipped,  the  balls  are  broken  and  the 
amalgam  packed  with  the  iron  pestle  into  one  solid  mass, 
that  around  the  sides  particularly  being  smooth,  so  as 
to  leave  no  thin  ridges  to  break  away.  When  it  is  all 
smoothed,  a  hole  is  bored  in  the  center  to  the  bottom, 
with  an  iron  rod,  to  act  as  a  vent  for  the  escaping  gases 
and  to  prevent  the  entire  mass  from  being  raised  by 
the  pressure  underneath  before  it  makes  its  own  vent. 
In  this  case  also  the  heat  during  the  last  of  the  operation 
is  raised  to  a  bright  red  so  as  to  anneal  and  partially  melt 
the  gold  and  so  hold  it  together.  When  it  is  melted  on 
the  spot,  the  balls  are  put  in  unbroken,  and  sometimes 
each  ball  is  wrapped  in  a  piece  of  cloth  or  paper.  The 
wrapping  is  unnecessary  and  only  a  false  idea  of  exces- 
sive carefulness,  which  results  in  the  distillation  along 
with  the  quicksilver  of  pyroligneous  acid,  and  this  very 
quickly  chokes  the  condensing  pipe  and  flours  the  quick- 
silver, hindering  the  operation  considerably. 

After  all  is  ready,  the  lute  of  wood-ashes,  with  or 
without  salt,  is  mixed  and  put  on  the  cover,  not  on  the 
retort;  the  cover  is  put  in  place  and  keyed  tightly,  and 
all  the  oozing  luting  is  scraped  off  and  smoothed  around 
the  joint. 

The  next  question  arises,  how  and  where  to  retort. 
Retort  out  of  doors,  or  under  an  open  shed,  where  there 
is  no  danger  of  tire.  Do  not  use  the  blacksmith  forge, 
because  too  much  heat  is  unconsciously  given  with  the 
bellows,  nor  a  furnace  into  which  the  retort  is  set,  as  the 
heat  is  not  under  control,  while  it  is  hard  to  remove  a 
heavy  and  hot  retort,  and  in  both  these  cases  no  direct 
heat  can  be  applied  to  the  bottom.  Make  a  tripod  with 
a  ring  into  which  the  retort  just  fits,  and  high  enough 
to  allow  a  good  fire  place  underneath.  This  can  be 


HINTS  ON  AMALGAMATION.  81 

made  by  any  blacksmith,  and  the  only  point  to  be  ob- 
served is  that  the  legs  shall  be  extra  thick  and  strong, 
to  withstand  any  bending  from  the  heat  and  weight. 
In  addition  to  the  welding  of  the  legs  to  the  ring,  put  one 
or  two  rivets  in  each  leg,  for  additional  security.  Fig. 
22  shows  this  tripod. 

The  tripod  is  set  within  distance  of  the  water  pipe  and 
the  retort  put  in  place,  the  hose  connected  and  the  re- 
ceiving kettle,  partially  filled  with  water,  is  put  at  a 
slight  inclination  with  the  end  of  the  condensing  pipe 
submerged  in  it  an  inch.  A  small  fire  of  shavings  and 
a  little  oily  waste  is  started  directly  under  the  retort. 
This  is  gradually  increased  with  either  pine  bark  or 
wood,  but  slowly  until  all  the  air  is  driven  out,  and  a 
little  quicksilver  begins  to  run.  Then  the  fire  is  in- 
creased and  the  retort  kept  at  a  cherry  red  till  no  more 
quicksilver  can  be  collected,  after  tapping  the  pipe. 
When  this  is  shown  to  be  the  case,  the  fire  is  withdrawn, 
the  pipe  taken  out  of  the  kettle,  and  the  cover  of  the 
retort  taken  off.  To  prove  that  no  more  quicksilver  is 
left,  take  a  cold  shovel,  wet  it  and  hold  over  the  open 
retort,  when  it  will  be  covered  with  a  white  film  if  any 
of  the  quicksilver  remains.  Before  the  retort  has  a 
chance  to  cool,  dump  out  the  retort  metal  into  a  pan 
set  on  an  iron  plate  or  directly  on  the  plate,  and  scrape 
out  any  adhering  gold.  The  gold  must  now  be  cool 
enough  to  handle  with  the  bare  hands,  before  it  is 
weighed,  or  a  correct  estimate  of  its  weight  is  not  ob- 
tained. It  should  be  porous  and  bright,  or  the  amalgam 
has  not  been  properly  cleaned. 

The  question  as  to  what  fuel  to  use  is  of  some  moment. 
Do  not  use  charcoal  or  coke,  even  though  on  account  of 
the  greater  heat  it  would  be  surmised  that  time  can  be 
gained.  The  top  of  the  retort  must  be  kept  as  hot  as  the 


82  HINTS  ON  AMALGAMATION. 

bottom,  and  this  can  only  be  done  with  a  fuel  which 
gives  strong  flames.  The  best  fuel  is  pine  bark,  but  if 
this  is  not  easily  available,  dry  wood,  either  pine  or 
other  soft  wood,  will  do  as  well.  The  wood  is  sawed 
into  two-foot  lengths  and  split  to  small  size.  When  the 
fire  is  well  started,  some  pieces  are  placed  under  the 
retort  between  the  legs  of  the  tripod,  and  a  complete 
circle  of  the  wood,  placed  on  end,  is  stacked  against 
the  ring  of  the  tripod,  which  forms  a  chimney  for 
draught  and  a  gradually  increasing  heat.  Frequently 
only  one  firing  is  necessary  when  placed  in  this  way. 

The  retort  metal,  if  shipped  direct,  is  now  wrapped 
carefully  in  paper  and  then  sewed  and  sealed  in  an 
ore  sack  of  canvas.  If  melted  on  the  premises  into  a 
bar,  we  can  use  the  assay  furnace,  provided  there  is  no 
special  furnace.  The  fuel  used  for  melting  is  either 
charcoal  or  coke,  the  latter  good  English  and  not  gas- 
house  coke.  The  coke  is  very  much  to  be  preferred. 
The  black-lead  crucible,  for  a  long  time  before  use, 
should  be  put  bottom  up  on  the  boiler  or  other  hot  place, 
to  get  thoroughly  dried  out.  It  is  then  put  into  the  fur- 
nace where  there  is  a  hot  fire  dying  out.  Here  it  is 
put  bottom  side  upwards,  and  left  to  be  annealed  till 
everything  is  cold.  It  is  then  ready  for  the  melting  of 
the  gold  attended  by  a  minimum  of  danger  as  regards 
cracking.  Before  the  retorting  is  completed  a  fire  is 
started  in  the  furnace,  and  the  crucible,  resting  on  a 
piece  of  brick,  is  placed  in  position.  The  fire  is  gradually 
increased  till  the  crucible  is  heated  almost  to  a  white 
heat,  and  the  supply  of  incandescent  fuel  just  reaches 
to  the  top  of  the  crucible.  The  retort  metal  is  now  put 
in  from  an  iron  scoop.  This  can  be  home  made  from 
rolling  a  thin  sheet  of  Russia  iron  so  that  it  has  a  smaller 
diameter  at  one  end,  or  a  scoop  that  can  be  purchased 


HINTS  ON  AMALGAMATION.  83 

ready  made.  The  crucible  is  filled  nearly  to  the  top 
with  the  retort  metal,  and  a  tablespoonful  of  a  mixture, 
containing  ground  borax  and  a  little  sand  or  ground 
glass,  is  at  once  added.  If  all  of  the  metal  cannot  be 
added  at  once,  the  first  charge  is  thoroughly  melted 
before  any  more  is  put  in.  On  each  subsequent  addition 
a  little  more  of  the  fluxing  material  is  used.  When  all  the 
metal  is  in  quiet  fusion,  the  supernatant  slag  is  skimmed 
off  by  means  of  gently  passing  a  coiled  rod  of  cold  iron 
(Fig.  23)  over  the  surface,  frequently  chilling  the  slag 
by  pressing  it  on  an  iron  plate,  or  slight  immersion  in 
water.  When  the  slag  is  removed,  the  graphite  pot  is 
lifted  from  the  fire  and  the  contents,  after  thoroughly 
stirring  and  mixing  with  a  paddle  made  from  old  crucible 
and  heated  in  fire  before  use,  are  carefully  poured  into  a 
mold  already  prepared  for  them.  This  mold  has  been 
first  smoked  evenly  by  inverting  over  a  fire  of  cotton 
waste,  coal  oil  and  pitch  or  rosin,  and  then  heated  as 
hot  as  possible  by  exposure  to  the  heat  from  the  top 
of  the  furnace.  As  soon  as  the  gold  has  been  poured 
a  pinch  of  candle  scrapings  is  thrown  on  top  and  the 
mold  is  covered  by  an  iron  plate  or  a  piece  of  wood  and 
left  to  chill.  When  solid,  but  still  red  hot,  the  mold 
is  inverted  and  the  gold  brick  at  once  immersed  in  a 
cold  pickle,  consisting  of  water  acidulated  with  sul- 
phuric acid.  When  cold  enough  to  be  handled  with  the 
bare  hands,  it  is  removed  and  scrubbed  with  a  brush. 
Any  projections  are  hammered  flat,  and  the  bar  is  ready 
for  chipping  and  weighing.  Even  if  no  assay  is  made 
at  the  mine,  always  chip  off  two  pieces  from  diagonally 
opposite  corners,  mark  them  with  date  and  number  of 
bar,  and  file  away,  as  a  precaution  against  any  future 
dispute.  Stamp  on  bar  number  and  weight  in  troy 
ounces;  but  it  is  advisable  to  abstain  from  putting  oij 


84  HIN'TS  ON  AMALGAMATION. 

fineness  of  bullion  or  its  value.  In  any  and  all  circum- 
stances the  buyer  will  have  it  remelted  and  assayed, 
and  it  is  better  for  the  seller  not  to  publish  so  widely 
his  own  knowledge  of  its  value. 

Practically  all  gold  bullion  from  placers  and  quartz 
mines,  saved  by  amalgamation,  contains  some  silver,  and 
this  has  to  be  separated  before  the  gold  is  ready  for 
coining  or  other  purposes.  This  cannot  be  done  at  the 
mine,  and  as  some  gold  is  lost  to  the  seller  in  remelting, 
it  is  of  advantage  to  ship  the  bullion  as  retort  metal, 
save  the  expense  of  fuel  and  the  loss  in  melting.  Under 
any  circumstances  a  fixed  charge  has  to  be  paid  to  the 
refiners. 

Louis  Falkenau,  State  assayer  of  San  Francisco,  tells 
us  that  if  the  slag  dipped  off  is  powdered  and  panned 
and  old  crucibles  treated  in  the  same  way,  there  is  no 
loss  in  melting.  And  also,  if  the  bar  has  been  properly 
melted  and  mixed,  the  chips  will  ensure  a  control  which 
he  considers  important. 


CHAPTER  V. 
CONCENTRATION. 

In  the  beginning  of  this  series  of  articles,  a  rapid 
summary  was  given  of  all  the  various  processes  em- 
ployed in  milling  that  seemed  to  be  of  moment.  The 
most  minute  details  have  been  explained  in  connection 
with  the  extraction  of  the  free  gold.  We  come  now  to 
the  consideration  of  the  valuable  residues  still  remaining 
in  the  pulp,  to  which  the  generic  name  of  sulphurets  has 
been  given.  As  the  financial  standing  of  gold  mining 
to-day  depends  exclusively  on  the  ability  to  extract  all 
the  value  in  the  ore,  most  careful  attention  is  paid  to 
the  concentration  of  these  sulphurets  at  a  small  expense 
from  the  worthless  rock  into  a  paying  and  portable 
product. 

Rival  states  have  waged  a  bitter  controversy  over  this 
matter  of  concentration,  contending  that  each  one's  spe- 
cial process  is  the  best  and  should  be  more  largely 
adopted  in  other  places.  We  refer  to  the  radical  variation 
in  mill  practice  as  pursued  in  certain  localities  of  Colo- 
rado and  in  California.  The  author  is  free  to  confess  that 
he  is  prejudiced  in  favor  of  the  California  method,  as 
giving  a  higher  percentage  ultimately,  in  all  the  sections 
so  far  investigated.  However,  the  method  must  be  abso- 
lutely correct  and  not  a  partial  adaptation. 

In  iron  and  copper  pyrites  (the  commonest  gold-bearing 
minerals)  the  majority  of  the  gold  is  still  in  a  metallic 
state,  microscopic  leaves  in  the  fractures  of  the  mineral, 
and  if  pulverized  to  sufficient  fineness  can  be  caught 

85 


86  HINTS  ON  AMALGAMATION. 

with  quicksilver,  but  the  expense  is  increased  in  a  pro- 
hibitive ratio,  owing  largely  to  the  small  duty  performed 
by  each  stamp  per  horse-power  consumed.  Again,  the 
sulphurets  have  been  so  depleted  of  their  values  that  it 
is  only  possible  and  advisable  to  save  them  where  they 
have  more  value  than  the  gold  they  still  contain,  and 
where  the  cost  of  concentration  can  be  done  without 
additional  expense  beyond  the  first  outlay  in  plant.  The 
first  condition  is  obtained  by  the  demand  of  lead  and 
copper  smelters  for  an  iron  flux,  and  their  nearness  to 
the  mines.  This,  and  this  only,  has  brought  the  Gilpin 
county  method  into  a  prominence  which  it  does  not  war- 
rant. Remove  the  smelters  from  Denver,  and  it  will  be  found 
to  be  economically  impracticable  to  save  the  concen- 
trates of  that  district  after  the  method  of  milling  em- 
ployed. We  are  not  trying  to  convert  the  millmen  of  that 
district  to  our  way,  but  the  majority  of  gold  mills  have 
not  the  good  fortune  to  be  in  such  close  proximity  to 
smelters,  and  it  is  suicidal  to  pursue  such  a  method  any- 
where unless  as  propitiously  situated.  The  Black  Hawk 
mills  save  an  average  of  80  per  cent.,  according  to  trust- 
worthy sources,  and,  we  honestly  believe,  this  percentage 
can  be  raised  to  over  90  per  cent,  and  at  a  less  expense 
per  ton,  if  they  will  stop  trying  to  corrall  every  speck 
of  the  free  gold  inside  the  mortar.  We  wish  to  be  very 
minute,  so  that  the  other  districts  of  the  world  can  judge 
in  regard  to  the  feasibility  of  the  process. 

We  have  mines  in  this  state,  in  which  the  ore  is  very 
simflar  to  that  of  Gilpin  county,  the  value  all  in  the 
sulphurets,  which  are  working  over  90  per  cent,  of  the 
assay  value,  and  at  a  less  cost  per  ton.  Of  these  the 
most  notable  is  the  "Golden  Gate,"  of  Tuolumne  county. 
We  would  advise  any  person  who  is  considering  the  rela- 
tive merits  of  the  two  processes,  to  make  some  inquiries 


HINTS  ON  AMALGAMATION.  87 

first,  not  from  the  manufacturers  of  the  machinery,  but 
from  the  owners  or  superintendents  of  some  of  the  sul- 
phuret  mines  in  this  State.  It  is  not  a  question  of  slow 
or  fast  drop,  but  of  high  or  low  discharge,  and  the  fine- 
ness of  the  mesh  of  the  screen. 

We  are  all  trying  to  save  as  much  of  the  value  in  the 
mill  as  possible  and  at  a  minimum  of  expense,  and  to 
do  this  we  have  to  harmonize  the  two  distinct  processes 
of  amalgamating  and  concentrating,  and  not  unduly 
favor  one  at  the  expense  of  the  other. 

Now  gold  has  a  very  high  specific  gravity  and  yet  be- 
comes so  fine  that  it  floats.  It  is  also  malleable,  but 
not  often  brittle,  and,  therefore,  is  comminuted  very  little 
after  being  freed  from  its  enclosing  gangue.  Sulphurets, 
on  the  other  hand,  have  much  less  specific  gravity, 
and  are  always  brittle,  which  brittleness  increases  di- 
rectly as  their  richness  in  the  precious  metals.  Expose 
fine  sulphurets  for  an  instant  only  to  the  air  and  they 
will  float  on  the  surface  of  the  water  for  miles  or  till 
submerged  by  the  water  falling  an  inch  or  more. 

Go  at  any  time  below  any  of  the  mills  of  the  Black 
Hawk  district,  except  immediately  after  a  heavy  storm, 
and  the  banks  of  the  gulch  will  be  found  lined  with  sul- 
phurets, while  in  the  eddies,  all  the  detritus  is  composed 
of  pure  concentrates.  Go  below  a  California  mill,  prop- 
erly handled,  and  only  traces  are  found  on  panning,  and 
none  is  seen  with  the  naked  eye.  The  assay  of  the  tail- 
ings for  each  ton  in  Gilpin  county  may  be  low,  but  the 
aggregate  in  a  year  that  can  be  saved,  is  so  large  that  it 
seems  almost  criminal  to  allow  such  a  loss  to  exist.  The 
keynote  of  this  loss  is  owing  to  the  unnecessary  sliming 
of  these  very  brittle  sulphurets.  First,  the  14  inches 
or  more  that  the  pulp  has  to  rise  through,  before  dis- 
charging, keeps  all  the  ore  to  be  struck  so  many  times 


88  HINTS  ON  AMALGAMATION. 

by  the  stamps  that  the  sulphurets  are  ground  to  a  slime 
and  this  is  secondarily  aided  by  the  fineness  of  the 
screen  openings,  but  only  partially,  as  we  have  very  fre- 
quently had  to  employ  a  No.  12  punched-slot  screen  on 
California  ores,  to  save  all  the  values.  The  output  of 
this  is  as  fine  as  that  of  a  50-mesh  wire  screen. 
£Now,  the  greatest  trouble  to  be  found  in  concentration, 
is  to  save  the  slimed  mineral,  and  often  the  slimes  are 
removed  with  a  point  box  and  settled  separately  in  order 
to  make  any  showing  at  all  satisfactory.  It  is,  there- 
fore, obligatory  to  crush  as  coarsely  as  is  consistent  with 
the  loss  in  the  tailings,  which  loss  must  be  located, 
whether  in  the  sand  or  slimes.  If  in  the  sand,  finer 
crushing  is  required  till  we  are  satisfied  we  have  reached 
the  most  practical,  that  is,  economical  efficiency.  Of 
course,  it  is  advisable  to  save  all  free  gold  possible  with 
the  quicksilver,  but  not  to  such  an  extent  as  to  ruin  the 
concentration  of  the  remaining  values.  No  matter  how 
fine  the  sulphurets  are  pulverized,  they  will  still  contain 
free  gold,  and  even  after  roasting  this  free  metal  will 
not  be  absorbed  by  quicksilver;  but  it  is  only  with  a 
chemical  agent  that  the  gold  is  saved.  If  impartially 
considered,  all  will  agree  that  the  object  of  stamping 
is  to  save  all  possible  value  in  the  mill,  and  the  observa- 
tion that  can  be  made  by  any  one  below  the  mills  em- 
ploying the  different  methods,  should  practically  prove 
the  advantage  of  the  process  employed  in  this  state. 

As  there  are  tricks  in  all  trades,  there  are  certain  points 
in  regard  to  the  handling  of  concentrators  and  their  pro- 
duct which  will  materially  add  to  the  efficiency  of  the 
work  performed.  With  some  styles  of  machines,  a  great 
advantage  is  gained  by  sizing  the  material  to  be  treated 
with  the  aid  of  "spitzlutten"  or  ascending  columns  of 
water  under  varying  pressure,  but  this  is  not  necessary 


HINTS  ON  AMALGAMATION.  89 

with  a  shaking  table  working  without  a  jar.  In  fact, 
unless  there  is  an  undue  proportion  of  clay  slimes,  the 
side-shake,  endless-belt,  machine  will  do  its  best  work 
on  ore  just  as  it  leaves  the  battery  screens,  and  sulphurets 
will  be  separated  by  the  machine  which  require  great 
care  and  ingenuity  to  save  after  its  deposition  in  the 
concentration  tank. 

A  vanner  in  perfect  working  order  should  show  the  fol- 
lowing state  of  affairs:  First,  no  jar  whatever,  on  plac- 
ing the  hand  on  any  part  of  the  upper  frame;  second,  a 
thickness  of  pulp  on  the  bed  below  the  ore-spreader  of  y2 
inch,  slowly  flowing  towards  the  foot  of  the  machine, 
with  a  smooth  surface  and  no  ripples,  and  this  current 
must  not  be  faster  on  one  side  of  the  machine;  third,  a 
sand  edging  on  each  side,  along  the  flange  of  the  belt, 
of  equal  width  and  not  to  exceed  2  inches;  fourth,  at 
the  foot  of  the  machine,  the  taiilngs  to  escape  towards 
the  middle  of  the  belt,  leaving  the  flanges  and  a  small  tri- 
angular section  of  the  belt  free  from  sand  and  exposing 
clear  rubber;  fifth,  the  sand  to  be  kept  in  view  up  to 
the  rear  side  of  the  clear  water  box,  but  showing  no  dry 
fingers;  sixth,  the  sulphurets  to  be  passing  over  the  head 
of  the  machine  in  bands  between  the  clear  water  jets  and 
showing  absolutely  no  sand  or  slimes;  seventh,  when  the 
belt  leaves  the  concentration  tank,  that  it  shall  be  cleaned 
of  all  the  sulphurets;  eigthth,  that  the  concentrates  de- 
posited in  the  box  and  saved  by  the  machine  shall  be  also 
saved  by  the  operator^  and  not  allowed  to  escape  in  the 
overflow  waterTl  •  <  ~i."\ 

First,  no  jar.  In  setting  up  the  machine,  the  posts  and 
sills  are  mortised  and  placed  in  position,  with  the  keys* 
driven  in  on  the  outside  of  each  post.  Then  the  shoul- 
ders on  each  post  are  cut  to  scant  width  and  full  depth; 
that  is,  for  a  4  foot  machine  the  measurement  between 


90  HINTS  ON  AMALGAMATION. 

posts  calls  for  5  feet  6y2  inches,  but  the  shoulders  are  cut 
to  give  a  distance  of  5  feet  6%  inches,  and  when  the 
lower  frame  of  the  machine  is  put  together  the  bolts 
are  driven  in  with  a  sledge,  almost  cementing  frame  and 
posts.  If  through  shrinkage,  later  on,  the  machine  gets 
loose,  iron  or  hard  wood  wedges  must  be  driven  in  to 
form  a  tight  joint.  The  two  rollers  underneath  the 
machine  must  have  no  lost  motion,  and  must  not  strike 
the  sides  of  the  lower  frame.  The  lost  motion  is  taken  up 
by  tightening  the  two  cross  tie  rods  equally.  The  pre- 
vention of  striking  is  accomplished  by  moving  the  roller 
either  way  till  it  clears  each  side.  This  is  done  by  loosen- 
ing the  nut  of  the  rod,  on  the  side  the  roller  should  go, 
and  tightening  the  nut  on  the  opposite  side  (the  one  which 
is  striking).  See  that  the  flat  springs,  on  which  the 
shaking  table  rests,  do  not  strike  the  lower  frame,  and 
where  one  does,  drive  in  the  lower  spring  support.  Take 
up  all  lost  motion  of  the  end  rollers,  by  the  gudgeon  caps, 
and  see  that  there  is  none  also  in  the  journals  and 
brasses  of  the  shaft,  nor  in  the  spur  wheel  and  spring 
crank  shaft.  Last,  but  most  frequently  overlooked,  ex- 
amine each  one  of  the  little  rollers  over  which  the  belt 
travels,  and  move  the  chairs  till  there  is  no  side  motion, 
but  that  they  will  still  turn  easily,  and  then  fasten  each 
chair  by  driving  a  wire  nail  or  two  into  the  upper  rail, 
in  front  of  the  chair. 

Second,  haye  a  proper  bed  of  pulp.  Put  a  straight  edge 
across  top  of  lower  frame  and  with  spirit  level  make  it 
practically  level  across,  and  then  place  machine  on  dead 
center.  Take  a  piece  of  wood  just  two  inches  long  and 
place  between  upper  rail  and  top  of  each  cross  piece  of 
lower  frame,  and  raise  or  depress  lower  supports  by  the 
bolts  passing  through  lower  frame,  till  this  wood  just 
passes  easily  under  lower  rail  everywhere.  The  small 


HINTS  ON  AMALGAMATION.  91 

roller  next  to  the  main  head-roller  is  raised  by  a  piece 
of  wood  a  half  inch  above  the  plane  of  the  table,  but  all 
the  other  rollers,  including  the  foot  main  roller,  must 
form  a  perfect  plane.  To  determine  this,  a  string  or 
straight-edge  is  placed  over  the  second  small  roller  from 
the  head,  and  carried  over  the  main  foot-roller.  Bach 
little  roller  is  made  to  touch  this,  being  raised  by  having 
a  piece  of  cardboard  put  under  the  chair,  or  lowered,  by 
cutting  out  a  slight  shaving  from  the  rail.  Discretion 
must  be  employed  to  change  only  those  chairs  that 
affect  the  entire  table.  Place  the  main  driving  shaft 
by  the  three  movable  boxes,  so  that  the  distance  be- 
tween outside  edge  of  lower  frame  and  inside  edge  of 
shaft  is  exactly  2  inches  %  and  1-32.  The  machine  is 
now  ready  to  start.  The  speed  of  the  side-shake  is 
first  tried  at  190  revolutions  per  minute,  and  the  lower 
ends  of  the  machine  equally  lowered  till  the  grade  is 
about  }4  inch  per  foot,  while  the  uphill  travel  is  started 
with  the  small  leather  belt  an  inch  from  the  small  end  of 
the  cone  pulley. 

The  pulp  is  now  turned  on  and  allowed  to  run  for  15 
minutes,  without  altering  the  machine  or  until  it  gets 
its  load.  If  too  light,  the  foot  is  raised  equally  on  both 
sides,  but  generally  it  has  to  be  lowered,  from  being  too 
flat.  The  water  is  fixed  at  a  minimum,  and  the  sand 
is  brought  up  to  the  water  box  by  increasing  the  uphill 
travel.  Each  machine  acts  a  little  differently,  so  each 
one  is  separately  regulated,  till  proper  grade  and  uphill 
travel  are  attained.  This  should  be  all  that  is  required 
to  put  the  belt  in  perfect  shape.  However,  at  times,  we 
find  a  wide  expanse  of  dry  sand  on  one  side,  and  a 
correspondingly  swift  current  on  the  other,  which  must 
be  at  once  remedied.  Knowing  that  everything  is  in 
perfect  order,  this  is  at  first  incomprehensible,  until 


92  HINTS  ON  AMALGAMATION. 

it  is  observed  that  the  strain  is^stronger  on  one  throw 
of  the  crank-shaft  than  on  the  other  and  the  sand  is 
sensitive  to  the  slightest  variation.  To  overcome  this, 
we  have  two  remedies,  the  first  and  simplest  to  remove 
and  bend  the  spiral  drive-spring,  at  the  head  of  the 
machine,  inclining  the  point  the  way  the  sand  is  wanted 
to  travel.  The  second  is,  to  move  the  entire  main 
shaft,  1-32  to  1-16  inch,  in  or  out,  as  the  case  requires; 
out,  if  the  heavy  sand  corner  is  on  the  same  side  as  the 
shaft,  and  in  if  the  reverse  is  the  case. 

Seventh.  In  order  to  be  sure  that  the  belt  is  cleaned  of 
sulphurets  after  leaving  the  main  tank  underneath  the 
machine,  two  series  of  jets  are  directed  against  it  above 
and  below,  and  the  pipes  must  be  frequently  watched 
to  see  that  the  holes  do  not  clog,  most  particularly  dur- 
ing the  time  when  the  accumulated  deposits  are  with- 
drawn, and  the  water  rapidly  lowered  in  the  tank  till 
it  may  not  submerge  the  belt.  It  is  also  very  necessary 
to  observe  when  we  lower  or  raise  the  machine,  that  the 
belt  is  not  either  raised  completely  out  of  the  wash 
water,  or  sunk  so  deep  as  to  cause  undue  agitation. 
When  raised  out  of  the  water,  the  conclusion  is  obvious. 
If  sunk  too  deep,  the  belt  and  flange  throw  the  water 
back  and  forth  so  violently  that  it  slops  over  the  sides 
of  the  box,  carrying  sulphurets  as  well  as  making 
everything  sloppy;  but  the  chief  fault  lies  in  the  fact 
that  the  concentrations  do  not  settle  here  but  are  carried 
away  with  the  overflow  water.  With  the  least  agitation 
too  much  escapes  in  this  way.  This  overflow  contains 
the  richest  in  value  as  well  as  the  finest  in  size  of  all 
which  is  saved  by  the  machine,  and  this  brings  us  to 
the  consideration  of  the  very  important  subdivision  No. 
8,  namely,  for  the  operator  to  collect  that  which  the  ma- 
chine has  saved.  It  is  important,  but  frequently  over- 


HINTS  ON  AMALGAMATION.  93 

looked.  The  mill  is  doing  good  work,  according  to  the 
assay  of  the  final  tailings,  but  the  product  does  not 
tally  with  these  assays,  owing  to  lack  of  care  of  the 
concentrates  after  the  machine  has  extracted  them  from 
the  pulp.  Some  minerals,  notably  nagyagite  and  black 
telluride,  largely  saved  by  the  machine,  will  float  as  a 
scum  on  the  water  of  the  tank,  and  run  away  with  the 
overflow  unless  it  is  forced  under  the  water,  and  the 
same  is  true  in  a  lesser  degree,  of  all  the  sulphurets. 
To  overcome  this,  we  always  place  a  piece  of  rubber 
belting  in  a  semi-circle,  around  the  inside  of  the  over- 
flow orifice,  which  extends  at  least  two  inches  below  the 
surface  of  the  water  in  the  tank.  This  requires  all 
the  material  to  be  thrust  under  the  water  before  it  can 
escape;  but  that  which  does  escape  should  flow  through 
a  very  long  series  of  dead-water  boxes,  in  which  are 
placed  numerous  obstructions  to  the  flow.  One  obstruc- 
tion is  to  place  cross-pieces  at  intervals  which  extend 
nearly  to  the  bottom  of  the  box;  while  another  obstruc- 
tion is  to  frequently  transfer  the  current  through  a  sur- 
face orifice  to  another  box  in  which  the  current  runs 
in  the  opposite  direction,  and  the  two  together  are  very 
efficient.  A  peculiar  slime  box  was  lately  brought  to  our 
observation,  in  conjunction  with  a  patented  slime  con- 
centrator, which  appears  to  be  of  exceptional  value, 
as  presenting  great  obstruction  to  the  flow  of  the  solid 
material  in  the  water.  We  append  a  sketch  of  this  as 
of  interest,  only  remarking  that  the  wings  are  remova- 
ble. (Fig.  24.) 

These  devices  prevent  as  much  loss  as  possible  in  the 
slimed  material  while  the  machine  is  running,  but  there 
are  other  losses  to  be  guarded  against  as  well.  Each 
machine  has  constantly  on  its  bed  a  greater  weight  of 
sulphurets  than  is  commonly  supposed,  which  remains 


HINTS  ON  AMALGAMATION. 


uniform  as  long  as  the  pulp  flows  on  it  and  it  is  kept  in 
agitation.  Stop  the  machine  and  pulp  and  allow  the 
water  to  run  and  this  accumulated  load  is  rapidly 
washed  into  the  tail-race,  a  total  loss,  unaccounted  for 
by  the  assays  of  the  tailings,  and  it  is  a  very  great  loss 
as  well.  So  that  on  stopping  the  machine  temporarily, 
always  turn  off  the  water  and  when  stopping  for  some 
time,  as  during  clean-up,  always  work  off  the  load  on 


*"/ 


*~E 

;  Eleva.it  on  !! 

tt  _ii  

Modern  Machinery . 

the  belt  before  stopping  the  machine.  A  third  source 
of  loss  is  the  careless  removal  of  the  concentrates.  Twice 
a  day  the  accumulations  are  hoed  out  into  a  drain  box, 
placed  in  front  of  each  machine,  and  the  surplus  water, 
after  settling  by  blows  or  stirring,  thrown  back  into  the 
concentration  box.  Be  sure  that  the  wheel-barrow  or 
car  is  water-tight,  and  do  not  fill  it  more  than  three 
fourths  full,  as  in  moving  it  becomes  almost  a  liquid, 
from  the  water  held  in  suspension.  Have  a  separate 
room  for  storage  which  is  tight,  and  save  all  spillings 
from  shoveling,  etc.,  as  they  count  in  a  year's  time. 

In  spite  of  the  most  careful  settling,  the  concentrates 
will  carry  at  least  10  per  cent,  of  moisture,  which  should 


HINTS  ON  AMALGAMATION.  95 

be  eliminated  as  a  matter  of  economy  if  for  no  other 
reason.  If  the  sulphurets  are  chlorinated  on  the  ground, 
this  excess  of  water  increases  the  consumption  of  fuel 
in  roasting.  Generally,  however,  the  concentrates  of 
one  mine  are  too  limited  in  quantity  to  warrant  the  erec- 
tion of  a  reduction  plant,  and  therefore,  they  are  period- 
ically shipped  to  smelter  or  other  custom  reduction 
works.  This  shipment  requires  long  wagon  hauls,  be- 
sides railroad  transportation,  for  which  the  expense 
charges  are  always  based  on  gross  weight.  It  is  easy 
to  see  the  loss  in  cash  returns  on  the  ore  when  at  least 
one-tenth,  and  often  one-fifth,  of  the  gross  weight  is 
barren  water,  which  can  be  removed  at  the  mill  before 
shipment  with  only  a  little  trouble  and  at  a  very  small 
expense.  If  dried  as  soon  as  removed  from  the  machine, 
the  sulphurets  do  not  oxidize,  clinker  and  cement  to- 
gether, but  allow  such  a  thorough  mixing  at  all  times 
as  to  get  accurate  sampling  and  assays. 

The  sun  is,  of  course,  the  cheapest  drier,  but  its  use 
is  of  doubtful  value,  if  the  concentrates  are  dried  on  a 
platform  in  the  open  air,  as  the  wind  will  very  quickly 
scatter  several  per  centum,  as  soon  as  they  become  dry. 
To  use  sun  heat,  a  room  must  be  constructed,  with  the 
three  sides  consisting  of  panes  of  glass  and  ventilator* 
in  the  roof.  In  other  words,  have  a  conservatory  with- 
out the  glass  roof.  This  room  need  not  be  very  large, 
as  the  concentrates,  as  soon  as  dried,'  are  shoveled  into 
a  storage  bin,  where  they  are  sacked,  sampled,  weighed 
and  shipped.  For  a  20-stamp  mill,  make  the  floor  20 
feet  by  30  feet,  putting  the  room,  if  possible,  on  the 
sunny  side  of  the  concentrator  room,  and  place  the  bin 
at  a  lower  elevation  than  this  floor. 

For  artificial  drying,  very  little  heat  is  required,  and  it 
can  be  procured  from  waste  steam,  or  any  scraps  of 


96  HINTS  ON  AMALGAMATION. 

wood  chips,  etc.,  that  are  handy.  The  top  of  the  drier  is 
made  of  sheet  iron  with  raised  sides.  When  the  sulphur- 
ets  are  nearly  dry,  they  will  run  like  quicksilver  on 
being  touched  or  stirred.  In  using  steam,  a  coil  of  pipe 
is  placed  underneath  the  plate,  which  comes  from  the 
engine  and  which  discharges  the  condensed  water  and 
steam  outside  the  building.  In  using  fire  direct,  it  is 
necessary  to  build  a  regular  drying  furnace,  with  a  rela- 
tively large  fire-box.  The  simplest  form  is  to  place  the 
iron  tray  directly  on  the  fire-box,  and  create  the 
draught  with  a  short  piece  of  pipe  at  the  further  end. 
However,  as  in  all  cases  it  is  better  to  do  well  anything 
that  is  undertaken,  we  would  advise  the  erection  of  a 
regular  drying  furnace.  This  will  consist  of  a  fire-box 
and  bridge  at  one  end  of  the  plate  and  a  shallow  space 
under  the  plate  from  the  bridge  to  the  flue,  all  to  be 
built  of  red  brick  and  fire  clay. 

As  soon  as  the  sulphurets  are  dry,  they  are  shoveled 
into  a  storage  bin,  till  wanted  for  shipping.  In  sacking 
them  the  closest  woven  canvas  should  be  used,  and 
before  each  sack  is  sewed  a  sample  is  taken  with  a  fryer 
such  as  used  to  sample  butter,  or  made  by  splitting 
a  half-inch  gas  pipe.  Another  satisfactory  method  is 
to  use  a  quarter-inch  auger.  Do  not  expect  any  check 
on  the  value  when  a  pinch  is  taken  from  the  top  of  each 
sack,  as  a  sample  must  extend  clear  to  the  bottom. 

As  stated  above,  the  slimes  taken  from  the  overflow 
settling  boxes  are  invariably  very  much  richer  than 
the  coarser  concentrates  which  are  collected  each  day, 
but  they  are  generally  very  limited  in  quantity.  On 
account  of  the  small  amount,  these  boxes  are  only 
cleaned  occasionally,  once  a  month  or  less  frequently. 
When  these  are  dried  by  themselves,  it  is  imperative 
that  they  shall  be  uniformly  scattered  over  and  mixed 


HINTS  ON  AMALGAMATION.  97 

with  the  accumulations  already  in  the  storage  bin,  or 
the  mine  is  never  credited  with  its  full  value.  If  sacked 
by  themselves,  the  one  or  two  samples  taken  of  them 
and  mixed  with  the  100  or  more  samples  from  the 
vaster  amount  of  the  coarser  accumulations,  will  not  be 
nearly  as  accurate  in  giving  the  average  value  as  if 
all  had  been  thoroughly  mixed  in  the  first  place,  and 
the  100  or  more  samples  should  each  contain  their  proper 
proportion  of  these  rich  slimes.  If  the  space  at  the  mill 
will  allow  it,  we  would  advise  sampling  as  done  by  'the 
smelters.  The  concentrates  are  shoveled  into  sacks,  but 
every  third,  fifth  or  tenth  shovelful  is  put  into  a  separate 
pile  till  all  the  concentrates  are  sampled.  If  the  result- 
ing pile  is  still  bulky,  every  other  shovel  is  put  into 
the  sacks,  and  then  the  remainder  is  shoveled  into  a 
cone,  spread  out,  and  quartered  down  till  the  assay 
weight  is  obtained.  With  the  necessary  appliances  this 
can  be  done  very  quickly.  Beside  a  broom  and  square- 
pointed  shovel,  there  are  required  a  sack-filler,  and  iron 
cross  for  both  of  which  ideas  we  are  indebted  to  a  well 
known  smelter  near  San  Francisco.  The  sack-filler  has 
been  copied  from  that  in  use  on  potato  ranches,  and  is 
an  iron  cylinder  with  a  funnel  top,  which  is  inserted 
into  each  sack.  (Fig.  25.) 

The  iron  cross  is  made  of  two  pieces  of  iron  at  right 
angles,  and  two  sizes  should  be  kept  on  hand,  both  in 
height  and  circumference.  With  this  cross,  each  shovel- 
ful is  dumped  directly  over  the  center  of  the  cross,  and 
on  smoothing  the  resulting  cone,  the  quartering  divis- 
ions are  already  accurately  determined,  of  uniform  size 
and  position.  (Fig.  26.) 


CHAPTER  VI. 

SAMPLING. 

It  is  of  very  rare  occurrence  to  find  an  assay  office 
attached  to  a  gold  mill,  but  if  any  intelligent  work 
is  done,  it  is  imperative  to  have  absolute  technical 
accuracy  at  frequent  intervals,  and  not  trust  entirely 
to  the  eye,  which  is  deceptive,  no  matter  how  finely 
trained.  In  silver  mills  and  other  reduction  works  a 
qualified  assayer  who  also  possesses  an  insight  of  the 
methods  in  metalliferous  chemistry,  is  absolutely  essen- 
tial to  the  success  of  the  enterprise.  Such  wide  techni- 
cal knowledge  is  not  demanded  in  gold-mill  practice, 
though,  of  course,  of  appreciable  benefit;  but,  the  su- 
perintendent or  one  of  the  employes  of  a  company 
must  be  able  to  make  an  accurate  determination  by 
fire  of  the  values  in  the  ore  and  tailings  when  required. 

Gold  is  worth  $20.67  per  ounce,  and  occurs  very  irreg- 
ularly disseminated  in  the  accompanying  gangue,  when 
in  a  free  state.  On  account  of  its  value,  a  small  particle 
in  that  piece  assayed,  might  enhance  the  estimated  value 
of  the  body  of  ore  under  investigation  much  beyond 
the  working  value  afterwards  determined  in  practice,  and 
the  opposite  results  might  also  erroneously  be  obtained. 
For  this  reason,  the  determination  of  the  value  of  free 
gold-bearing  quartz  in  place,  by  sampling  and  assay,  is 
a  very  uncertain  method  of  fixing  the  value  of  a  mine, 
and  yet  it  is  the  one  universally  employed  by  experts,  and 
these  experts  in  general,  are  entirely  unfamiliar  with  the 
existing  conditions  of  that  particular  section,  As  pre- 


HINTS  ON  AMALGAMATION.  99 

liminary  information,  sampling  of  a  mine  and  fire  as- 
says, are  very  necessary,  but  before  a  definite  conclusion 
is  arrived  at,  wherever  possible,  a  practical  mill-test 
of  25  to  100  tons  should  be  employed,  the  ore  for  which 
is  taken  from  all  parts  of  the  mine,  without  sorting, 
and  just  as  it  would  be  worked  permanently  on  a  large 
scale.  If  under  no  circumstances  can  such  a  mill  test 
be  made,  we  advise  this  method  of  procedure.  The  ex- 
pert comes  to  the  property  and  makes  a  rapid  survey  of 
the  interior  workings  of  the  mine,  and  the  character  of 
the  wall  rocks,  strike,  etc.  Then  he  will  examine  the 
general  surface  geology  of  the  country,  and  by  inquiry 
and  observation,  determine  the  prevailing  conditions  of 
that  section.  This  can  be  seen  by  the  operations  of 
neighboring  mines,  if  there  are  any  that  are  working 
or  have  been  exploited.  With  the  deductions  he  makes, 
after  sifting  out  notable  inaccuracies  due  to  ignorance 
or  jealousy,  it  is  now  with  a  common-sense  foundation 
of  the  general  conditions  that  he  is  able  to  devote  his  in- 
quiries to  the  one  mine  in  view.  A  few  pieces  of  the  ore 
from  different  parts  are  first  taken,  crushed  in  a  hand 
mortar,  and  panned,  to  determine  the  character  of  the 
gold,  whether  coarse  (when  it  is  probably  very  un- 
evenly distributed),  or  fine  and  floured,  which  would 
imply  a  more  uniform  dissemination.  Of  course,  the 
number  of  samples  taken  must  be  in  great  abundance, 
near  together,  and  each  of  large  size,  and  the  maximum 
distance  between  samples  should  not  be  over  8  to  9  feet. 
If  fine,  and  several  hundred  feet  of  quartz  have  been 
exposed,  we  are  generally  safe  in  an  average  value,  if 
the  samples  are  taken  every  20  feet.  In  every  case, 
each  sample  must  be  taken  completely  across  the  ledge, 
either  by  blast  or  maul,  and  everything  mixed  and  quar- 
tered down  to  the  size  required  without  using  any  dis 


100  HINTS  ON  AMALGAMATION. 

cretion  or  selection,  as  that  is  the  way  it  would  be  prac- 
tically worked  in  a  mill.  If  practicable,  have  a  small 
assay  crusher,  and  reduce  the  coarse  uniformly,  as  the 
quartering  proceeds,  thoroughly  mixing  after  each  reduc- 
tion in  the  size  of  the  pieces.  A  diagram  of  the  mine 
where  each  place  is  sampled,  with  its  corresponding 
number,  is  entered  in  the  note  book,  and  the  samples  are 
sacked  and  sent  to  the  assayer  for  tests,  but  each  sam- 
ple should  weigh  5  pounds,  and  15  pounds  is  better.  We 
wish  to  state  at  this  point  that  the  value  of  a  mine  is 
not  always  determined  by  sampling,  but  it  is  the  only 
resource  on  which  an  expert  foreign  to  the  conditions 
of  a  certain  section,  can  rely  for  his  first  judgment 
of  the  property,  while  it  is  the  natural  preliminary  to  a 
practical  mill-test.  Should  the  vein  be  too  large  to  ad- 
mit of  taking  one  sample  across  its  width,  a  series  of 
samples  are  taken  in  each  cross-section  at  absolutely 
equal  distances  apart  in  every  case. 

After  the  assayer  returns  the  individual  values  to  the 
expert,  he  is  able  to  lay  out  accurately  the  length  and 
direction  of  the  ore-shoot  or  shoots,  in  the  mine,  and 
whether  the  ledge-matter  intervening,  has  a  value  that 
would  warrant  its  exploitation  without  reducing  the 
total  output  prohibitively.  He  now  instructs  the  assayer 
to  take  a  weighed  proportion  of  each  sample,  good  or 
bad,  that  occurs  in  the  ore-shoot,  and  make  a  laboratory 
working-test,  on  amalgamation  and  subsequent  concen- 
tration. This  will  serve  as  a  guide  for  a  final  mill  test, 
but  only  as  a  guide,  as  the  mechanical  work  of  the  mill 
will  generally  give  better  results  than  any  hand-test 
made,  though  only  in  total  value  saved,  and  not  nec- 
essarily in  an  increase  of  either  the  free  gold  or  sul- 
phurets.  Unless  frequent  and  large  samples  from  the 
mine  are  taken  as  stated  above,  the  resultant  mill  work 


HINTS  ON  AMALGAMATION.  101 

will  be  very  disappointing  to  the  owners,  and  detrimental 
to  the  reputation  of  the  expert  himself,  unless  the  blame 
is  laid  on  a  supposedly  faulty  mill.  This  is  frequently 
done,  and  very  unjustly,  if  a  good  amalgamator  is  in 
charge.  Grab  samples  of  a  few  selected  pieces,  judged 
by  the  eye,  to  be  both  average,  poor  and  the  highest 
grade,  can  be  assayed,  and  a  test  of  the  ore  in  25-ton 
lots  run  through  the  mill,  and  the  resulting  product  be 
found  to  be  not  over  60  per  cent,  of  what  was  expected 
from  the  average  of  the  selected  samples,  when  accusa- 
tions of  dishonesty  are  hinted  at  and  often  expressed. 
It  seems  to  be  an  accepted  axiom  amongst  mine  owners 
that  "a  custom  mill  will  always  cheat,"  when  the  fault 
lies  entirely  with  themselves  in  estimating  what  ought 
to  be  returned,  according  to  the  assays  of  one  or  two 
little  pieces  of  rock,  and  human  nature  will  force  them 
to  take,  if  not  the  better  looking  rock,  at  least,  clean  ore, 
neither  of  which,  it  is  readily  seen,  can  be  any  criterion 
of  a  mass  of  ledge  blasted  down  and  always  carrying 
more  or  less  of  the  barren  country  rock  which  has  to 
be  handled  with  the  clean  quartz,  on  wnch  they  form 
their  judgment. 

I  have  gone  so  fully  into  a  matter  that  does  not  seem 
to  be  pertinent,  because,  as  mentioned  above,  the  mills 
are  generally  so  unjustly  blamed.  Several  years  ago, 
I  was  requested  by  a  prominent  railroad  man,  to  make 
a  working  test  in  a  neighboring  mill,  on  25  tons  of  ore 
from  a  mine  he  held  under  bond.  While  the  ore  was 
being  brought  to  the  mill,  I  was  asked  to  make  three 
assays,  one  of  a  highly  mineralized  piece  of  rock  weigh- 
ing less  than  a  pound,  and  supposed  to  be  so  high-grade 
that  similar  rock  was  not  shipped  to  the  mill,  but  was 
sorted  out  for  sale  to  smelter.  The  second  sample  was 
one  piece  of  about  %  pound  weight,  taken  from  the 


102  HINTS  ON  AMALGAMATION. 

mine  and  considered  about  average,  while  the  third  sam- 
ple was  their  average  of  this  entire  lot  and  consisted  of 
four  little  pieces  of  clean  quartz.  After  making  the  as- 
says and  finding  the  highest  grade  did  not  go  over 
$10  per  ton,  while  the  average  of  the  three,  even  in- 
cluding this  one,  was  under  $8  per  ton,  I  examined  the 
ore  that  had  already  been  stored  in  the  bin  and  was 
positive  it  would  not  stand  up  to  the  assays.  Therefore, 
to  protect  myself  beforehand,  I  informed  this  gentleman 
that  I  wished  him  to  bear  in  mind  a  common  report  that 
custom  mills  invariably  retained  a  part  of  the  proceeds 
for  their  personal  aggrandizement.  On  the  completion 
of  the  test,  the  resultant  amalgam  netted  $3.50  per  ton, 
the  concentrates  $1  per  ton,  and  the  final  tailings  35c. 
per  ton,  giving  a  total  of  $4.85  per  ton  of  ore  treated. 
On  making  my  report  the  question  was  immediately 
asked,  why  the  returns  were  so  low,  when  the  average 
of  the  preliminary  assays  showed  $8  per  ton;  but,  calling 
to  my  help  the  previous  statement  and  the  required  ex- 
planation placed  the  situation  most  forcibly  before  this 
gentleman.  It  is,  therefore,  well  to  have  a  most  thor- 
ough sampling  of  the  mine,  or  trust  entirely  to  the  sam- 
ples taken  in  the  mill. 

Assays  during  the  steady  run  of  a  mining  property  are 
rarely  taken  in  California,  except  in  the  case  of  foreign 
corporations,  and  it  is  a  very  great  mistake.  The  ex- 
pense of  an  adequate  outfit  is  very  slight,  at  a  maximum 
price  of  $500,  and  the  cost  of  all  the  assays  per  month, 
would  make  no  material  difference  in  the  profit,  while  'n 
many  cases  great  losses  would  be  prevented.  The  com- 
mon practice  is  to  guess  at  the  value  of  the  ore,  and  the 
loss  in  final  tailings,  by  panning.  Though  it  is  not  im- 
perative to  assay  by  fire  all  the  ore  of  a  free-gold  mine 
dally,  yet  an  occasional  assay  of  a  new  stope  opened,  or 


HINTS  ON  AMALGAMATION.  108 

any  change  in  the  character  of  the  quartz  is  a  very 
great  help.  This  same  sample  should  be  panned, 
and  then  becomes  an  approximate  guide  to  the 
value  of  the  different  samples  that  must  be 
panned  down  each  day  by  the  foreman  or  in 
case  of  a  large  property,  the  employe  especially  appoint- 
ed for  that  purpose.  In  the  Homestake  property,  one 
man  is  kept  steadily  at  work  panning  and  estimating 
the  free  gold  value  of  over  one  hundred  samples  each 
day.  The  method  employed  there,  is  to  weigh  out  a  cer- 
tain portion  of  each  sample  and  pulverize  it  to  an  im- 
palpable powder  in  a  hand  mortar,  filled  with  water,  the 
crushing  being  done  by  a  pestle  attached  to  a  power  drill. 
The  resultant  pulp  is  panned,  and  the  values  of  the 
gold  judged  by  the  eye  alone,  is  entered  in  the  report 
book.  By  constant  practice,  the  accuracy  attained  on 
that  ore  is  remarkably  correct,  but  the  same  man  on 
another  property  would  require  several  assays  before  he 
would  become  as  adept  in  agreeing  so  closely.  Again, 
this  will  give  only  the  free  gold,  and  is  of  absolutely 
no  value  in  determining  the  gross  amount  of  gold  in  the 
ore,  where  a  fire  assay  alone  can  be  of  any  benefit. 
Therefore,  in  regard  to  the  ore  in  a  free-milling  prop- 
erty, be  sure  and  have  occasional  assays,  and  do  not  trust 
entirely  to  the.  eye. 

Coming  down  to  the  mill,  we  find  a  very  different  sit- 
uation where  a  very  close  estimate  of  the  value  of  the 
quartz  can  be  obtained,  often  by  taking  periodical  sam- 
ples from  the  self-feeders,  and  always  accurately  by 
samples  below  the  plates  and  adding  to  the  values  of 
the  assays,  the  amount  of  free  gold  collected. 

Several  devices  for  automatic  sampling  have  been  in- 
vented, but  from  the  fact  that  it  is  the  exception  to 
see  any  of  them  employed,  it  is  conceded  that  ordinary 


104  HINTS  ON  AMALGAMATION. 

hand  sampling  is  as  correct,  gives  less  trouble,  and  is 
always  available.  Hand  sampling  has  its  points  to  be 
observed  to  insure  accuracy  and  very  few  appreciate 
the  wherefore  that  it  should  be  done  in  one  way  more 
than  another.  To  get  a  sample  of  the  quartz  before 
entering  the  battery,  it  must  be  taken  as  it  leaves  the 
feeder  to  enter  the  throat  of  the  mortar.  Use  a  dipper, 
and  see  that  the  same  quantity  each  time  drops  into  it. 
Be  sure  and  be  regular  in  time,  either  a  half-hour  or 
hour,  that  each  sample  is  taken,  and  at  the  end  of  the 
specified  number  of  hours,  reduce  the  whole  systematic- 
ally by  finer  crushing,  mixing  and  quartering.  The 
reason  that  the  outlet  of  the  self-feeder  is  the  only  safe 
place,  is  that  the  ore  is  here  the  most  thoroughly  mixed 
and  crushed  to  a  more  uniform  size.  Car£camples  aie 
only  grab  samples,  a  little  taken  at  random  from  the  top, 
generally  the  finer  pieces,  or,  if  a  coarse  piece  is  taken, 
too  great  a  proportion  for  that  time.  From  the  car 
the  ore  is  separated  by  the  grizzly  into  the  fines  and 
coarse,  but  the  coarse  is  broken  by  the  crusher,  and, 
in  passing  through  the  ore  bin.  becomes  fairly  well 
mixed  with  the  fines.  It  is  then  remixed  in  passing 
through  the  automatic  feeder,  and,  being  delivered  by 
that  to  the  battery  in  such  a  small  quantity  and  thin 
stream,  all  of  the  ore  for  that  instant  is  caught  in  each 
sample.  We  consider  this  sample  of  small  importance, 
as  we  get  immediate  returns  from  the  free  gold,  and  it  is 
only  the  value  locked  up  in  the  sulphurets  that  would 
probably  escape  us,  which  we  can  only  determine  after 
the  free  gold  is  extracted.  Therefore,  the  important 
sampling  begins  at  the  end  of  the  plate  surface.  We 
have  two  places  at  our  command,  at  the  inlet  and  at  the 
outlet  of  the  trap.  It  is  unsafe  to  trust  a  sample  taken 
below  the  lower  apron  plate  as  there  is  always  the  pos- 


HINTS  ON  AMALGAMATION.  105 

sibility  of  a  little  amalgam  being  broken  off  in  passing 
the  dipper  along  the  edge  of  the  plate.  If  it  can  be  done 
and  the  whole  stream  covered,  the  inlet  to  the  trap  is  the 
better  place,  as  the  outlet  may  carry  more  sulphurets 
than  the  average  at  one  time  or  the  other.  The  under- 
current will  accumulate  sulphurets  to  a  ceratin  depth, 
when  the  increased  pressure  will  throw  them  out  in  a 
bunch,  and  the  process  is  begun  over  again.  In  taking 
all  these  samples,  a  separate  dipper  must  be  kept  for 
pulp,  as  well  as  for  tailings.  No  overflow  whatever  is 
allowed,  and  the  sample  is  put  in  a  covered  can,  while 
the  dipper  is  thoroughly  rinsed  out  each  time.  The 
jar  of  the  mill  will  very  rapidly  settle  all  the  solid  matter 
when  the  clear  water  is  very  carefully  poured  off,  al- 
lowing none  of  the  slimes  to  escape.  In  very  exceptional 
cases  it  will  be  advisable  to  evaporate  all  this  water 
for  a  comparative  test,  but  the  difference  will  be  found 
to  be  imappreciable.  At  the  end  of  the  time  set,  the 
resultant  sample  is  thoroughly  dried,  mixed,  quartered 
down  and  assayed.  Should  a  regular  daily  assay  be 
made,  which  will  give  a  correct  weekly  average,  it  is 
only  necessary  after  pouring  off  the  supernatant  liquid, 
to  mix  most  thoroughly  the  residual  slimes  into  a  con- 
sistent mass,  and  then,  while  stirring,  take  out  a  dip- 
perful  and  dry  that  for  the  assay. 

The  most  important  sample,  and  the  only  one  abso- 
lutely necessary  in  a  gold  mill,  is  that  of  the  tailings  as 
they  leave  the  mill.  These  should  be  taken  each  hour 
from  the  foot  of  each  machine,  and  never,  under  any 
circumstances,  from  the  waste  sluice  where  there  might 
be  a  partial  reconcentration  of  the  tailings.  The  dipper 
is  drawn  steadily  across  the  foot  with  no  pause  at  either 
end  where  a  great  proportion  of  the  tailings  leave  the 
machine.  This  sample  is  settled  and  manipulated  as 


106  HINTS  ON  AMALGAMATION. 

\ 

described  for  the  pulp,  but  at  the  time  each  one  is 
taken,  a  duplicate  should  be  examined  by  panning,  to 
see  the  amount  of  visible  sulphurets  escaping.  The  fore- 
man should  compare  the  assays  of  a  sample  with  a 
panning  test  of  the  same,  and  after  several  examples 
can  approximately  determine  tLe  good  or  bad  working  of 
any  particular  machine,  from  panning  alone.  In  mak- 
ing these  tests,  the  color  of  the  sulphurets  are  so  different 


Modern  Machinery.  FIG.  27. 

from  that  of  gold,  that  they  do  not  show  on  a  dark 
ground,  and  they  are  so  fine  and  light  that  more  care 
must  be  exercised,  and,  in  reality,  a  different  method 
employed.  The  best  color  is  pure  white,  and  where 
nothing  better  offers,  a  tea-saucer  is  far  preferable  to 
a  gold-pan.  However,  now,  there  can  be  procured  white 
enameled  pans  of  all  sizes,  but  choose  those  with  very 
flaring  sides.  A  patented  instrument  is  now  specially 


HINTS  ON  AMALGAMATION.  107 

made,  by  which  the  faintest  trace  of  sulphuret  can  be 
detected.  The  idea  originated  from  the  Cornish  van- 
ning shovel,  used  in  the  tin  mines,  where  all  assays  are 
made  by  hand  concentration  of  the  sample.  Similar 
in  shape  to  an  ornamental  plaque,  it  is  called  a  vanning 
plaque.  It  is  a  circular  segment  of  the  surface  of  a 
globe,  and  is  made  of  wrought  iron,  covered  with  a 
homogeneous  coating  on  both  sides  of  white  enamel. 
The  method  of  using  this  is  different  from  that  of  a 
pan  or  saucer,  in  that  the  plaque  is  always  held  nearly 
horizontal.  The  tailings  are  settled  by  swinging  it  hori- 
zontally and  then  allowing  a  wave  of  clear  water  to  pass 
over  the  surface  with  this  same  circular  motion.  When 
the  tailings  have  been  reduced  to  a  minimum  without  any 
loss,  the  plaque  is  held  firmly  in  the  two  hands  at  a  steep 
angle,  and  by  a  series  of  jerky  throws,  the  heavy  sul- 
phurets  climb  up  the  inclined  plane,  and  can  then  be 
collected  in  a  string  of  colors  by  gently  washing  the  re- 
maining sand  away.  (Figure  27.) 

In  regard  to  the  concentrates,  the  only  reliable  assay 
is  of  the  bulk  when  prepared  for  shipment,  but  a  close 
approximation  can  be  obtained  by  taking  numerous  sam- 
ples with  the  butter-trier  or  augur,  from  the  settling  box 
in  front  of  the  machine,  after  the  water  has  been  re- 
moved. It  is  unsafe  to  make  any  definite  conclusion 
from  a  sample  taken  off  the  belt. 


CHAPTER  VII. 
CONCLUSION. 

With  the  suggestions  in  the  foregoing  pages  taken  .~s 
a  basis,  it  should  not  be  difficult  for  any  one  to  adapt 
them  to  the  local  conditions  so  as  to  increase  the  efficien- 
cy of  the  work,  and  to  correct  unknown  losses.  Put 
in  a  concise  form,  the  summary  would  be. 

1st.    Beware  of  grease. 

2nd.    Amalgamate  dry. 

3rd.  Turn  over  the  pulp  as  frequently  as  possible 
near  the  battery. 

4th.  Use  all  necessary  water  inside  the  battery,  and 
do  not  divide  it  with  a  spray  outside. 

5th.  Have  the  battery  water  warm,  at  least  above 
a  minimum  temperature  of  50  degrees,  better  above  70 
degrees. 

6th.  Use  no  acids  on  the  plates,,  nor  lye  or  cyanide 
inside  the  battery. 

7th.  Dress  the  plates  at  least  one  a  day,  but  remove 
as  little  of  the  amalgam  as  can  be  prevented  till  clean-up. 

8th.    Most  thoroughly  clean  the  daily  amalgam  at  once. 

9th.  Systematize  regular  clean-ups  and  do  not  remove 
unnecessary  dies. 

10th.  Retort  out  of  doors  and  do  not  use  charcoal  or 
coke  for  fuel. 

llth.  See  that  the  concentrators  work  noiselessly  and 
without  a  jar. 

12th.  Watch  the  tailings  of  the  concentrators  and  see 
that  the  loss  from  the  mill  is  kept  at  a  minimum. 

108 


HINTS  ON  AMALGAMATION.  109 

13th.    Be  very  sure  that  your  ore  is  adapted  to  the 
free-milling  process. 

(All  gold-bearing  ore  is  not  adapted  to  the  free-milling 
process,  and  on  opening  a  mine  this  point  must  be  defi- 
nitely determined  before  the  reduction  works  are  erected. 
An  assay  will  determine  the  value,  a  panning  test  will 
demonstrate  if  any  of  the  gold  is  free,  and  a  laboratory 
working  test  will  inform  us  of  the  amount  that  can  be 
expected  to  be  saved  by  amalgamation  and  concentra- 
tion; but  if  the  final  tailings  are  still  very  high,  some 
method  has  to  be  found  to  recover  this  value.  Should 
the  highest  percentage  remain  in  the  tailings,  cyaniding 
must  be  tried,  or  chlorination,  if  the  gross  value  of  the 
ore  will  stand  the  expense,  while  sometimes  a  combina- 
tion of  all  must  be  used.  If  the  ore  is  very  high-grade 
and  refractory  as  well,  smelting  of  the  mass  is  the 
proper  procedure.  Neither  cyanogen  or  chlorine  will 
economically  act  on  coarse  gold,  and  both  processes 
require  crushing.  If  our  panning  tests  show  coarse  gold, 
and  the  value  is  too  low  for  smelting,  we  have  to  crush, 
and  then,  either  before  or  after  the  chemical  work,  can 
secure  the  coarse  gold  by  amalgamation.  The  great- 
est detriment  to  successful  milling  is  the  presence  of  tel- 
lurium compounds,  except  the  telluride  of  lead  and  cop- 
per. These  cannot  be  amalgamated  or  concentrated  to 
a  practical  efficiency,  and  yet  if  these  ores  as  usual,  show 
great  richness  in  free  gold  and  coarse  gold,  they  are 
milled,  and,  as  a  consequence,  hundreds  of  thousands  of 
dollars  are  run  to  waste,  all  of  which  would  have  been 
saved  if  the  whole  mass  had  been  shipped  to  a  smelter. 
Therefore,  examine  the  ore  for  tellurium,  and  if  of  suf- 
ficient richness,  ship,  even  though  at  the  same  time  rich 
in  free  gold. 

In  Tuolumne  County,  California,  many  of  the  mines 


110  HINTS  ON  AMALGAMATION. 

have  chimneys  of  ore  very  rich  in  free  gold  and  tellurides,  j 
and  the  early  history  of  a  few  of  them,  show  that  they" 
were  formerly  abandoned,  though  known  to  be  rich, 
because  so  little  of  the  value  could  be  saved.  One  mine 
can  be  specially  mentioned  as  a  type,  namely,  the  Black 
Oak.  This  mine  very  nearly  ruined  its  owners,  by  the 
attempt  to  work  by  free-milling  alone,  was  bonded  twice 
and  abandoned,  and  within  two  years  from  this  time, 
had  been  offered  on  long  bond  for  a  small  figure.  To- 
day, it  cannot  be  bought,  since  means  have  been  found  to 
save  the  $10  to  $50  per  ton  previously  lost.  No  special 
method  has  been  devised,  but  reduction  was  at  last 
adapted  to  common  sense.  Instead  of  using  the  mill 
process  as  the  sine  qua  non,  the  ore  is  now  partially  sort- 
ed, the  richest  shipped  direct  to  the  smelter,  the  balance 
crushed  wet  by  mill,  amalgamated  and  concentrated. 
!_The. tailings  are  impounded  and  worked  by  cyanide  pro- 
cess, and  the  concentrates  shipped  to  smelter. 

On  ores  which  are  purely  adapted  to  concentration,  it 
becomes  very  frequently  a  delicate  question  whether  to 
employ  stamps  or  some  other  crushing  device.  In  this 
case,  the  object  is  to  have  the  grains  of  sulphurets,  while 
absolutely  freed  from  the  gangue,  in  as  large  a  size  as 
possible,  and  with  a  minimum  of  slimes.  Stamp  mills 
for  amalgamating,  make  a  larger  proportion  of  slimed 
mineral  than  Cornish  rolls  and  devices  of  the  type  of  the 
Chilian  mill,  for  the  reason  that  the  pulp  will  escape 
from  the  latter  forms,  as  soon  as  crushed  to  the  re- 
quired fineness,  while,  owing  to  the  height  of  discharge 
in  a  stamp  mill,  quite  a  proportion  is  struck  several 
times  before  escaping.  Here  the  character  of  the  ore  can 
be  divided  into  two  classes:  Class  A,  in  which,  if  it 
is  found  that  the  ore  carries  enough  free  gold  to  pay 
working  expenses,  the  process  as  minutely  described  in 


HINTS  ON  AMALGAMATION.  Ill 

the  foregoing  pages  must  be  employed;  class  B,  in 
which  the  ore  contains  no  free  gold  of  moment.  Stamps 
are  employed  on  hard  ore  in  which  the  mineral  is  finely 
disseminated  through  the  matrix.  The  discharge  is  in- 
stantaneous, and  the  mortar,  being  merely  a  crushing  de- 
vice, is  patterned  after  that  in  use  in  silver  mills.  If  the 
ore  is  soft  and  shows  great  tendency  to  slime,  roller  mills 
are  the  proper  machines  with  vanners  to  do  the  concen- 
trating. ' 

The  subject  is  endless,  and  as  a  science,  gold  metal- 
lurgy is  still  in  its  infancy.  However,  we  trust  that  the 
above  hints  will  be  of  some  help  in  the  one  branch 
of  this  science  that  has  been  considered  in  these  pages. 


UNIVERSITY 

CALIFOH 


THE     END. 


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